In Act 1 of Othello, how does Iago use persuasion to scheme against Othello?

Look at Act 1 Scene 3, after close-reading it and the summary. After Desdemona's wish is granted, Roderigo is despairing,feeling he has lost her for ever. Iago sees this and ever-observant and waiting to pounce sees the weaknesses and motivations of the others too. He becomes excited as a plan is sparked - he shares his evil manipulations in his speech at the end of the Act so examine that line by line and use some quotes:

He fills Roderigo with false hopes 'put money in thy purse' (cheer up, get ready to be rich and happy-your fortunes are about to change)

'thou shalt enjoy her'

'Let us be conjunctive in our hate against him'

'thine hast no less reason'

and Iago...tellingly...in 'private'

'thus do I ever make my fool my purse'

'Cassio's a proper man: let me see now to get his place.....'

and about Othello - it will be easy to manipulate him and

have him 'led by the nose as asses are' by putting pressure on his suggestible nature.

Why are they all so blind? Previous question about this below:

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In Act 1 of Othello, how does Iago use persuasion to scheme against Othello?

In Act 1, Iago uses different forms of manipulation with each character so that he can advance his scheme to bring down Othello and Cassio.

Roderigo: Iago knows that Roderigo is controlled by his emotions and, therefore, not a logical thinker.  He first "pinpoints the enemy" with Roderigo by telling him that Othello has just eloped with Roderigo's love interest Desdemona.  After painting Othello as an unequal match for the fair heroine, Iago stirs up Roderigo's anger toward the Moor and convinces him to awaken Brabantio to tell him that his daughter is gone.

Brabantio: With Brabantio, Iago also pinpoints the enemy by describing Othello, who has run off with Brabantio's only child, in unflattering animalistic terms.  Iago's diction is also carefully chosen to inflame Brabantio's feelings toward Othello.  He refers to Othello's skin color and other stereotypes from his day to remind Brabantio how others will view Desdemona's running off with the Moor.

Othello: With Othello, Iago panders to his every move.  He puts on a completely different face and appears to be a loyal and honest confidant for the general.  His most effective means of persuading Othello to trust him is simplyhis appearing to show respect to his leader. He strokes Othello's pride by reassuring him that the Duke and Senate will not hold his marriage to Desdemona against him because of his great skill and reputation with them.

In Othello, act 3, how does Iago incite Othello's jealousy?

In Othello, Act 3, Scene 3, Cassio visits Desdemona to beg for her assistance in getting his position back. While he is leaving Desdemona, Othello sees Cassio and questions whether or not that it was Cassio:

Wasn’t that Cassio leaving my wife?

At this point, Iago plants a seed of doubt in Othello's mind. He begins to express that Cassio is sneaking away:

Cassio, my lord! No, sure, I cannot believe
That he would steal away so guiltily,
Seeing you coming.

In this manner, Iago is trying to make Othello jealous. He plants seeds of suspicion in Othello. Immediately, Othello becomes suspicious. 

Next, Iago begins to plant seeds of doubt about Desdemona's character. He mentions to Othello that she lied to her father once:

She deceived her father by marrying you;

By this point, Othello is thinking seriously about Iago's accusations. Othello admits that Iago is right:

And so she did.

Now, Othello is becoming jealous. Iago has set the green-eyed monster free. Iago is cunning, crafty. He has planted seeds of doubt and suspicion. Now, Othello is in a position to see what Iago wants him to see. Before long, Othello will be consumed with jealousy until he cannot escape it. Iago has done what he set out to do.   

How does Iago manipulate Othello in Act 3, Scene 3?

In act 3, scene 3, Iago poisons Othello's mind, insinuating that Desdemona's been cheating on him with Michael Cassio. It's a total lie, of course, but Iago is such a skilled manipulator that he's able to make his lies sound so utterly plausible. Iago has taken a perfectly innocent situation and completely distorted it to make it seem like there's something untoward going on. Cassio has asked Desdemona to intercede on his behalf with Othello, to get him restored to favor after his recent public disgrace. Desdemona gladly agrees; she's an old friend, and of course will do whatever she can to help.

When Othello and Iago arrive, Cassio hastily departs. He's still embarrassed about his behavior the previous night and so doesn't want to stick around. But Iago immediately sees an opportunity to put his wicked plan into action and takes it:

Ha! I like not that.

With these simple words, Iago plants the seeds of doubt in Othello's mind. He makes it seem that Cassio's hasty departure and obvious embarrassment are related to his courting of Desdemona. Iago doesn't come right out and tell Othello that he thinks Desdemona and Cassio are having an affair; he's much too devious and clever for that. Instead, he resorts to insinuation and snide innuendo to inflame Othello's jealousy. Othello picks up on Iago's suspicions and demands to know what he's thinking:

Nay, yet there’s more in this. I prithee speak to me as to thy thinkings, As thou dost ruminate, and give thy worst of thoughts The worst of words.

Iago's response is a master-class in fake servility:

Good my lord, pardon me, Though I am bound to every act of duty I am not bound to that all slaves are free to. Utter my thoughts? Why, say they are vile and false, As where’s that palace whereinto foul things Sometimes intrude not?

Yes, I have my suspicions about Cassio and Desdemona, says Iago, but it's best not to say them out loud. For one thing, I might be completely wrong.

Iago knows that the longer he refuses to reveal what's on his mind, the more determined Othello will become to find out what his suspicions are. And when Iago finally does spill the beans, as it were, he does so in the guise of a dear friend, filled with sorrow at having to share such suspicious thoughts with someone who means so much to him. But even then, he still speaks in a suggestive, indirect manner. Iago knows that if he can continue to plant seeds of doubt in Othello's mind, then they'll grow of their own accord:

Look to your wife, observe her well with Cassio. Wear your eyes thus, not jealous nor secure.

Iago's seemingly inexhaustible capacity for doublespeak is much in evidence here. Although he urges Othello not to be jealous, at the same time, he's actually fanning the flames of that jealousy by encouraging him to keep a close eye on Desdemona and Cassio. Once Othello takes him up on his suggestion, Iago will be in a perfect position to execute the next stage of his wicked plan: concocting "evidence" to prove Desdemona's infidelity.

How does Iago manipulate Othello in Act 3, Scene 3?

Othello "divorces" Desdemona in this scene and effectively "marries" Iago by the end of it.

Iago's web of treachery has taken over three of Othello's "senses": hearing, sight, and language.  Like Oedipus, Othello is deaf, dumb, and blind to the truth.

First, Iago appeals to Othello's ear by planting how Desdemona and Cassio have be cheating on him behind his back.  This riles Othello's jealousy, and the "green-eyed monster" takes over Othello's emotions, limiting his use of reason and language.

Next, Iago gives Othello "ocular proof" of Desdemona's betrayal by linking the handkerchief with Cassio.  The handkerchief, once a symbol of Desdemona's love, now becomes one of betrayal.  Iago has managed to let everyone get their hands on the handkerchief; it goes from Othello to Desdemona to Emilia to Iago to Cassio to Biancha.  It travels from a virgin to a "whore."  When Biancha brings in the magic hanky, Othello resolves to kill both Cassio and Desdemona.

Finally, Iago reduces Othello to a trance-induced "horned beast" who utters monosyllabic nonsense.  The once-mighty Othello of Act I, who argued so well against Brabantio, who used words instead of violence, whose speech was filled with wondrous pathos, now sounds like Brabantio from Act I:

Damn her, lewd minx! O, damn her!

O, blood, blood, blood!

I'll tear her all to pieces.

O monstrous! monstrous!

Iago proves that he who controls language controls people.  Iago has Othello by the strings, and he schemes to have his puppet strangle Desdemona in bed, which should be reserved for eros (physical love); instead, it will be a place of theros (death).

How does Iago manipulate Othello in Othello's Act 3, Scene 3?

This scene brilliantly features the way that Iago taunts Othello with fears that are half-formed and preys upon the jealousy that he knows Othello already suffers from. Note the way in which he asks a seemingly innocent question, raising an idea in Othello's mind, and then overtly does his best to avoid talking about it again, in spite of Othello's demands that he share his concern:

Did Michael Cassio, when you wooed my lady,

Know of your love?

And it is this question that enflames Othello's jealousy. The way that Iago repeats the words of the questions that Othello asks him in particular drives Othello insane, leading him to suspect that Iago believes that something is going on between his wife and Cassio. Note what Othello says to Iago:

By heaven, thou echo'st me

As if there were some monster in thy thought

Two hideous to be shown. Thou dost mean something...

Iago never names his fears, but the way in which he raises his concerns causes Othello to think the worst. Such a subtle approach from Iago allows Othello to play right into his hands. Iago, because of his "love" for Othello and the confidence that he has, is able to win his ear and thus set the stage for the way that he poisons Othello's mind against Cassio and his wife.

How does Iago manipulate Othello and Desdemona in Act 4?

In Act 4 of Shakespeare's The Tragedy of Othello, Iago's villainy is most apparent in the outcomes of his earlier schemes, but he does continue to manipulate Othello and Desdemona in fiendish ways that intensify the drama.

For example, in scene 1, Iago makes repeated insinuating comments to Othello without accusing Desdemona of infidelity directly. This manipulation makes Othello jealous and rageful because it stimulates his imagination in cruel and damaging ways. When Iago finally lies, specifying that Cassio has been with Desdemona, Othello cannot cope with this information and is overwhelmed.

In scene 2, Desdemona confides in Iago about Othello's confusing accusations, suggesting that someone must have planted terrible ideas in Othello's head about her fidelity. Iago manipulates Desdemona in this moment, minimizing Othello's emotional state and explaining his irrationality as a consequence of work-related stress.

How does Iago manipulate Othello and Desdemona in Act 4?

At this point in the play, Othello has become convinced that Desdemona gave away his handkerchief. Iago pretends to defend her by saying her handkerchief is hers to give. He keeps reminding Othello of the token. Iago draws out Othello’s curiosity by saying that Cassio has bragged about his affairs. Then he frustrates Othello by not immediately telling him exactly what Cassio has admitted. The graphic suggestion that Cassio lies “With her [Desdemona], on her; what you will,” and that he undermines Othello’s reputation by telling people this, sends Othello into an epileptic seizure.

Iago talks to Cassio where Othello can see but not entirely hear the conversation. Iago assures Othello that Cassio is mocking Desdemona, when he is actually talking about his lover Bianca. Coincidentally, Bianca barges in and accuses Cassio of giving her “some minx's token,” Desdemona’s handkerchief. This makes Cassio look even worse—he got the handkerchief from a married woman and then, according to Iago, “hath given it his whore.” Whenever Othello leans towards leniency, Iago steers him away from the idea. Even poisoning the innocent Desdemona isn’t enough for Iago: “Do it not with poison, strangle her in her bed, even the bed she hath contaminated.”

Othello is so worked up about Cassio that he rages over an order for Cassio to take his place in Cyprus. He lashes out at Desdemona, who still speaks well of Cassio, thinking that she is sleeping with him. Because Iago is so close to Othello, Emilia and Desdemona turn to him for help. Iago feigns confusion, attempts to dispel the possibility that “Some base notorious knave, some scurvy fellow” has lied to Othello, and suggests that only “The business of the state does him offence.” It is the beginning of the end for everyone involved.

How does Iago manipulate Othello and Desdemona in Act 4?

Iago is able to create gross and vivid images of Desdemona with Cassio which cause Othello such torment that he has a seizure. This is shocking for the audience as we see Othello lose both physical and mental control at the word of Iago who implies that Cassio will-

lie … with her, on her; what you will.

He convinces Othello that he will be able to overhear Cassio talking about his relationship with Desdemona. The audience is aware that Cassio is talking about Bianca, however, when he says how she dotes on him-

She was here even now; she haunts me in every place.

Iago has convinced Desdemona  that she should appeal to Othello to reinstate Cassio. She is not aware of Othello’s suspicions of  a union between her and Cassio, and unwittingly angers him until he strikes her .

How does Iago provoke Othello's jealousy in Act 4?

I agree mostly with the first response given by another eNotes educator, but I would like to add a few important points from the beginning of the first scene in Act IV. In the first scene, Iago simply uses cryptic speech and hypothetical question to incite Othello’s further jealousy.

First, Iago is suggestive at asking a hypothetical question which is if someone could be naked and in bed with someone while not meaning any harm. Othello’s response is rife with jealousy:

Naked in bed, Iago, and not mean harm! / It is hypocrisy against the devil!

Iago, then puts this image in to Othello’s mind when this has most certainly not happened with his wife Desdemona and anyone else other than her husband. Iago then incites Othello even further by reminding Othello about the handkerchief. Iago mentions that any gift, like a handkerchief, that is a present from a husband, could be given away to any other man. Othello then suddenly “remembers” that he saw Cassio with the handkerchief that Othello had given to Desdemona.

It is at this point that Iago uses some very cryptic speech when he says that “what he did” was “lie.” When Othello questions further about how that is so, Iago replies “with her, on her, what you will.” This, combined with the first two incriminating ideas, makes Othello fall down into “a trance.”

In conclusion, we can’t leave out Iago’s use of Cassio. A later scene in act four is what the former educator is speaking about: Iago asks Othello to hide in order to observe Cassio speaking. It is important to note, however, that Cassio is speaking about Bianca and not about Desdemona. Othello has no idea, and this indicates an example of dramatic irony: a time when the reader/watcher knows something that the character doesn’t.

How does Iago provoke Othello's jealousy in Act 4?

Iago continues to build Othello's jealousy through use of Cassio.  For example, when Iago and Cassio speak about Bianca, Iago leads Othello to believe they were speaking about Desdemona, so Othello is further angered by hearing Cassio speak negatively about "Desdemona" (really Bianca).  Another example is when Iago tells Othello that he should believe that Desdemona has slept with Cassio when he says that Cassio has lain "...with her, on her; what you will.”  Othello has become so enraged that he strikes Desdemona for no apparent reason.  His complete fall has nearly taken place when Iago tells him that he should strangle her in her bed.

What does Iago say about Othello's jealousy to Desdemona in act 4?

Iago is a clever, yet evil, mastermind in William Shakespeare’s great tragedy Othello. Iago is working quickly to plot against Othello, the Moor. One of Iago's plots is to present a fictitious story that a soldier, Cassio, is having a romantic affair with Othello’s wife, Desdemona. Of course, Othello becomes jealous when he hears of this.

Concerned about her husband’s jealousy, Desdemona asks Iago for help. She cannot understand why Othello is treating her unkindly or why he has called her a “whore.” She pleads for Iago's assistance. Iago quickly denies Othello’s jealousy, not wanting to reveal his evil plan. He tells her:

I pray you, be content, ‘tis but his humor.
The business of the state does him offence. And he does chide with you.

Essentially, Iago is fooling Desdemona by pretending he is comforting her. He tells her not to worry about Othello’s words and that he is simply in a poor mood. He says that the country’s political state is concerning Othello, and he is taking his frustrations out on his wife.

Desdemona trusts Iago's words and does not bring her concerns to Othello. Iago ultimately succeeds in his plan, which leads to Desdemona’s unfortunate death.

What does Iago say about Othello's jealousy to Desdemona in act 4?

He says that it must be some business about the war or something else that is really bothering him:

I pray you, be content; 'tis but his humour: The business of the state does him offence,

And he does chide with you.

There is no way that Othello, who loved Desdemona so dearly, could really have any problem with Desdemona.  Of course Iago must also be sure that she doesn't get a real hint as to what is happening because she might explain it and then Othello might see the truth!

How is Iago manipulative in Othello?

Iago is an interesting villain. Whereas many of Shakespeare's villains—like Macbeth, Lady Macbeth, Angelo (in Measure for Measure), Tamora (in Titus Andronicus), and Richard III—generally take care of business themselves or directly order someone else to do it, it's not until the last act of Othello that Iago does anything to get his own hands dirty. Even then, Iago gets personally involved only because his plan against Othello goes slightly awry, and he has to step in to sort things out by wounding Cassio and murdering Roderigo in act 5, scene 1. Later, in act 5, scene 2, Iago kills his own wife, Emelia, for revealing his plan to destroy Othello and Desdemona, but this occurs only after his plan has already succeeded. Until then, Iago is content to manipulate others into doing his dirty work.

Iago is a master of insinuation and deception, and he uses those skills to take advantage of other characters' weaknesses and insecurities. Othello is a trusting soul, and Iago insinuates himself into Othello's trust— "I know thou'rt full of love and honesty" (3.3.134), "My friend... honest, honest Iago" (5.2.185). Iago also recognizes that Othello has a dangerously jealous nature, and he insinuates to Othello that Desdemona is unfaithful to him after Othello sees Cassio talking with her and quickly leave the scene when Othello enters.

IAGO. Ha! I like not that.

OTHELLO. What dost thou say?

IAGO. Nothing, my lord; or if I know not what.

OTHELLO. Was not that Cassio parted from my wife?

IAGO: Cassio, my lord! No, sure, I cannot think it,
That he would steal away so guiltylike,
Seeing you coming. (3.3.37-43)

In act 4, scene 1, Iago deceives Othello with a staged conversation with Cassio that leads Othello to believe that Cassio is talking about Desdemona, when in fact Iago and Cassio are talking about Bianca, a prostitute who's in love with Cassio.

Unlike other Shakespeare villains who have clearly defined motives and objectives for their villainy (like wanting to be King of England or of Scotland, for example), Iago seems to lack a convincing motivation for wanting to destroy Othello and Desdemona.

IAGO. I hate the Moor. (1.3.379)

There's a racist motive involved, but it's difficult to know if it's Iago who's racist—he constantly refers to Othello as "the Moor"—or if Iago is simply playing on the prejudices of other characters like Desdemona's father, Brabantio.

IAGO. 'Zounds, sir, you're robb'd! For shame, put on your
gown;
Your heart is burst, you have lost half your soul;
Even now, now, very now, an old black ram
Is tupping your white ewe. Arise, arise!
Awake the snorting citizens with the bell,
Or else the devil will make a grandsire of you.
Arise, I say!

...[Y]ou'll have your
daughter covered with a Barbary horse; you'll have your
nephews neigh to you; you'll have coursers for cousins,
and gennets for germans. (1.1.91-97, 126-127)

Iago was passed over by Othello for the position of lieutenant, and he resents Othello for promoting Cassio instead of him. (1.1.8-33) This has nothing whatsoever to do with Desdemona and seems a rather insubstantial motivation for everything that Iago perpetrates against Othello in the play. Iago also thinks that his wife, Emilia, might have been unfaithful to him with Othello, but Iago doesn't seem particularly upset by that possibility and dismisses it.

IAGO. ...And it is thought abroad that 'twixt my sheets
He has done my office. I know not if't be true;
But I for mere suspicion in that kind
Will do as if for surety. (1.3.397-400)

Later in the play, Iago uses Emilia's supposed infidelity to rationalize his lust for Desdemona and his desire to destroy Desdemona along with Othello.

IAGO. Now, I do love her too,
Not out of absolute lust, though peradventure
I stand accountant for as great a sin,
But partly led to diet my revenge,
For that I do suspect the lusty Moor
Hath leap'd into my seat; ...

And nothing can or shall content my soul
Till I am even'd with him, wife for wife;
Or failing so, yet that I put the Moor
At least into a jealousy so strong
That judgement cannot cure. (2.1.299-310)

Nevertheless, Iago has no deep or profound reasons for his all-consuming hatred of Othello. The few reasons that Iago confides to the audience and to other characters serve only to justify his behavior rather than to support any substantial motivations for his actions.

Quite simply, Iago doesn't need any reason for his malicious, destructive behavior other than his desire to take revenge on anyone who crosses him or gives him even the slightest provocation.

How is Iago manipulative in Othello?

In Othello, Iago is extremely manipulative. Iago is a master at manipulation. Through his mere words, he plants seeds of doubt in Othello. Truly, Iago is subtle in his accusation as he merely suggests that Cassio may be having an affair with Desdemona. No doubt, Iago manipulates the situation to convince Othello that his wife is unfaithful with Cassio. When Cassio and Desdemona are merely talking, Iago leads Othello to the scene. As Othello views the scene, Iago plants seeds of doubt and jealousy in Othello. He uses hesitation as he speaks. This causes Othello to question what Iago is really saying. With Othello's insistence, Iago gives in and expresses his dislike of Cassio and Desdemona talking to one another:

Ha! I don’t like that.

When Othello questions Iago in saying, "What did you say?" Iago begins scheming. Iago pretends to be hesitant in his accusations:

Nothing, my lord.

Artfully and cleverly, Iago is causing Othello to think that Cassio and his wife should not be talking.

When Cassio realizes that Othello is coming, he quickly leaves the scene. Iago uses this moment to make Othello think that Cassio is stealing away because he is guilty of having an intimate talk with Othello's wife. Iago comments about Cassio quickly fleeing from the scene:

I cannot believe
That he would steal away so guiltily,
Seeing you coming.

Later on, Iago uses Cassio's genuine support of Othello to tempt  Cassio to become intoxicated, thus causing him to brawl with Roderigo. Of course, Iago is a master manipulator:

Come, lieutenant, I have
a bottle of wine; and here outside are a number of
Cyprus gents that would happily drink a round to the
health of black Othello.

Although Cassio initially refuses to drink, Iago uses his gift of scheming and talks Cassio into getting drunk.

After setting the scene, Iago moves on to further his evil plot. After Cassio and Roderigo fight, Othello releases Cassio from his position as lieutenant. Iago furthers his devious plan by manipulating Desdemona. Using Desdemona's prime weakness, naivety, Iago puts Cassio up to seeking Desdemona's help in getting his position as lieutenant back.

With the scene set, Othello begins to believe his beautiful Desdemona has been unfaithful with Cassio. Iago realizes Othello's insecurities and benefits by them. Othello is too trusting of Iago. Iago ever so subtly points out that Desdemona is capable of lying:

She deceived her father by marrying you;

Iago is a crafty manipulator. He definitely causes Othello to question Desdemona's integrity. At the same time, Iago assures Othello that he has only discredited Desdemona because of his love for Othello:

I hope you will consider that what I have spoken
Comes from my love;

Iago craftily apologizes for loving Othello too much:

I humbly beg your pardon
Because I was loving you too much.

Convinced of Iago's love, Othello states that he is forever indebted to Iago:

I am bound to you forever.

No doubt, Iago is a master at deceit. Iago is an excellent actor. He is convincing in his false sincerity. Because of Iago's expert manipulation, Othello smothers his beautiful wife.   

How does Iago convince Othello of Desdemona's infidelity?

In act 3, scene 3, Iago suggests to Othello that it is suspicious that Desdemona, a white woman, did not try to marry a white man, somebody of "her own clime (and) complexion," but instead chose to marry Othello, a Black man. In seventeenth-century England, white people were considered superior to Black people, and so interracial marriages were deemed unnatural. Indeed, Iago suggests that Desdemona's choice to marry Othello, a Black man, points to something "unnatural" in her character. By this, Iago means to imply that Desdemona is not to be trusted. Iago also reminds Othello that, according to the social hierarchy of the time, he, Othello, is inferior to Desdemona because of their respective skin colors. In this way Iago plants seeds of doubt in Othello's mind—doubts about Desdemona's fidelity and doubts about his marriage.

Once Iago leaves the stage, Othello laments that

I am black
And have not those soft parts of conversation
That chamberers have.

From this, we can infer that Othello, at least to some degree, believes the contemporary racist stereotypes about Black people. He believes that because he is Black, he is inferior. This insecurity is what makes him vulnerable to Iago's suggestions. Indeed, it is this fundamental insecurity that Iago manipulates to help him convince Othello that Desdemona could be unfaithful. It is by manipulating this insecurity in Othello that Iago convinces Othello that it would only be natural for Desdemona to be unfaithful and exchange him, a Black man, for a white man like Cassio.

After Othello demands "ocular proof" from Iago, meaning proof that he can see with his own eyes, Iago decides to give him that proof in the form of a handkerchief. He gets hold of a handkerchief that Othello has given to Desdemona, and he plants this handkerchief in Cassio's room. He then engineers a scenario in which Othello sees Cassio with the handkerchief, and from this moment on, Othello is convinced. Othello believes that Desdemona has given this handkerchief to Cassio as a sign of her love for him. This handkerchief is the final proof that Othello needs, and it drives him mad. He loses all of his ability to think rationally, and he becomes all the more easy for Iago to manipulate.

What quotes demonstrate Iago's manipulations in Othello?

Firstly, the fact that Iago declares his intention to harm Othello when he speaks to Roderigo, is a good quote:

I follow him to serve my turn upon him

Iago clearly and unambiguously says here that he only shows obedience to Othello to fool him into believing that he is being loyal and servile so that he may plot his downfall - true to the expression 'Keep your enemies closer.'

In the same speech he tells Roderigo:

... Others there are
Who, trimm'd in forms and visages of duty,
Keep yet their hearts attending on themselves,
And, throwing but shows of service on their lords,
Do well thrive by them and when they have lined
their coats
Do themselves homage: these fellows have some soul;
And such a one do I profess myself. 

It is obvious in these lines that Iago has much admiration for the type of servant who only obeys his master out of show and not because of genuine respect or duty. His sole purpose is to serve his own needs - they do homage to themselves. Such persons show spirit and Iago perceives himself to be the same. A confession of his devious and pernicious nature.

Iago has planned to rouse Brabantio, the beautiful and chaste Desdemona's father, to inform him that Othello had kidnapped her. The plan is to upset Brabantio to such an extent that he would take action against Othello. When the two arrive at his house, Iago shouts that there were thieves around. When Brabantio wakes and enquires what all the noise is about, Iago declares:

Zounds, sir, you're robb'd; for shame, put on
your gown;
Your heart is burst, you have lost half your soul;
Even now, now, very now, an old black ram
Is topping your white ewe. Arise, arise;
Awake the snorting citizens with the bell,
Or else the devil will make a grandsire of you:
Arise, I say.

Iago uses the most disgusting animal metaphors to inform Brabantio that his daughter is being sexually abused. He cleverly refrains from mentioning the so-called abuser by name, but makes indirect references to Othello. He is incessant and continues using these images to further shock Brabantio, who later seeks out the duke and demands Othello's arrest.

Iago later maliciously informs Othello about how badly Brabantio had spoken about him:

Nay, but he prated,
And spoke such scurvy and provoking terms
Against your honour
That, with the little godliness I have,
I did full hard forbear him.

He tells Othello that Brabantio criticized him at length and used such shocking and provocative references that he, Iago found it difficult to restrain himself from lashing out at Brabantio. Iago has now manipulated both men and ruined, in a very short time, the good relationship (though superficial) that existed between the two.

Iago also masterfully manipulates the foolish Roderigo to do his bidding by dangling the fact that he would help him pursue Desdemona's affections and win her over in front of him like a carrot. He tells Roderigo:

Thou art sure of me:--go, make money:--I have told
thee often, and I re-tell thee again and again, I
hate the Moor: my cause is hearted; thine hath no
less reason. Let us be conjunctive in our revenge
against him: if thou canst cuckold him, thou dost
thyself a pleasure, me a sport.

He tells Roderigo that they should work together against Othello. In this venture, both will achieve what they want - he revenge and Roderigo Desdemona.

There are many other examples of Iago's manipulations but the one which stands out particularly since it finally convinces Othello of Desdemona's 'infidelity', is Cassio's speech with Bianca. Iago had planted Desdemona's handkerchief in Cassio's room and he is now speaking to him. Othello is in hiding, eavesdropping. Cassio speaks:

She was here even now; she haunts me in every place.
I was the other day talking on the sea-bank with
certain Venetians; and thither comes the bauble,
and, by this hand, she falls me thus about my neck--

Othello thinks that Cassio is speaking about his wife, but he is speaking about Bianca. She arrives later and angrily confronts Cassio:

Let the devil and his dam haunt you! What did you
mean by that same handkerchief you gave me even now?
I was a fine fool to take it. I must take out the
work?--A likely piece of work, that you should find
it in your chamber, and not know who left it there!
This is some minx's token, and I must take out the
work? There; give it your hobby-horse: wheresoever
you had it, I'll take out no work on't.

When Othello sees the handkerchief, he is fully convinced that he has been cuckolded. His mind is made up and he sets in motion the tragic events which transpire later.

How does Iago exploit Othello's insecurities and vulnerabilities?

Even with all of his personal achievements and military accomplishments, the title character of Shakespeare's Othello demonstrates character flaws and deep-seated insecurities that Iago exploits to cause Othello's downfall.

Othello is a prideful man. When Iago enlists "three great ones of the city" (act 1, scene 1) to intercede on his behalf with regard to Othello's selection of an ensign, Iago remarks that Othello sends them away without even listening to what they have to say.

IAGO. But he [Othello], as loving his own pride and purposes,
Evades them with a bombast circumstance
Horribly stuff'd with epithets of war.
(act 1, scene 1, lines 12–14)

Othello has already decided who he wants as his ensign—he chooses Cassio, not Iago—and he's simply not interested in anyone else's opinion once he's made up his mind.

Iago uses this pride, stubbornness, and decisiveness to keep Othello focused on his revenge against Cassio and Desdemona for what Othello has convinced himself is Desdemona's infidelity.

Iago is able to lead Othello to the conclusion that Desdemona has been unfaithful to him with Cassio because Othello is insecure about his marriage to Desdemona. Othello feels unworthy of Desdemona, and he questions why Desdemona would choose to marry him over someone of “her own clime, complexion and degree” (act 3, scene 3)—someone like Cassio.

Once Iago has convinced Othello that Desdemona has been unfaithful to him, Iago inflames Othello's character flaw of jealousy to drive Othello toward the murder of Cassio (who escapes being killed) and Desdemona.

Iago manipulates Othello's insecurities and influences his behavior by planting seeds of uncertainty, distrust, suspicion, and jealousy in Othello's mind.

Iago is a very subtle villain. He performs very little of his villainy overtly—such as killing Roderigo and Emilia—and even then he acts overtly only when it's absolutely necessary to protect himself and his own interests.

Instead, Iago uses innocent-sounding leading questions, insinuation, and innuendo to manipulate Othello, sometimes with as little as a single word: "Indeed!" (act 3, scene 3). Iago also uses insinuation to cause Othello to doubt his own judgment of Cassio's character.

IAGO. Did Michael Cassio, when you woo'd my lady,
Know of your love?

OTHELLO. He did, from first to last: why dost thou ask?

IAGO. But for a satisfaction of my thought;
No further harm.

OTHELLO. Why of thy thought, Iago?

IAGO. I did not think he had been acquainted with her.

OTHELLO. O, yes; and went between us very oft.

IAGO. Indeed!

OTHELLO. Indeed? ay, indeed. Discern'st thou aught in that?
Is he not honest?

IAGO. Honest, my lord!

OTHELLO. Honest! ay, honest.

IAGO. My lord, for aught I know.
(act 3, scene 3, lines 105–118)

Iago focuses Othello's suspicions on Cassio and arouses his self-destructive emotions toward Cassio and Desdemona by suggesting the opposite.

IAGO. For Michael Cassio,
I dare be sworn I think that he is honest.
(act 3, scene 3, lines 141–142)

One seed that Iago plants in Othello's mind ultimately determines the fate of all of the major characters in the play:

IAGO. O, beware, my lord, of jealousy!
It is the green-eyed monster, which doth mock
The meat it feeds on.
(act 3, scene 3, lines 187–189)

How does Iago exploit Othello's insecurities and vulnerabilities?

Roderigo is a well-to-do and somewhat foolish man whom Iago manipulates and ruthlessly uses as a tool for his own purposes. Roderigo's main pre-existing vulnerability is his love for Desdemona. Iago convinces him he can still have her as a lover, despite her marriage to Othello.

Roderigo is insecure about his own ability to obtain Desdemona without Iago's help. Iago says frankly to Roderigo in act I, scene 3 that if he can cuckold or cheat Othello by persuading Desdemona to sleep with him, it will make Iago happy:

If thou canst cuckold him [Othello], thou dost thyself a pleasure, me a sport.

However, Iago also encourages Roderigo to depend on him to help him woo Desdemona. Iago, for example, manipulates Roderigo into giving him a good deal of money to buy gifts for Desdemona to help soften her towards him. However, as Iago reveals in act I, scene 3, he is simply keeping the money:

Thus do I ever make my fool [Roderigo] my purse [money supply].

By act IV, Roderigo is catching on to the fact that Iago is using him and not delivering Desdemona, despite all the money Roderigo has given him. Roderigo accuses Iago of always having some excuse to put him off, saying in act IV, scene 2,

Everyday thou daff’st me with some device.

But even at this point, smooth talking Iago is able to manipulate Roderigo. He uses flattery, telling him in act IV, scene 2 that he has faith in Roderigo as courageous. He says that if Roderigo can show his courage this night, by the night after he will be in bed with Desdemona—if not, he can kill Iago for his treachery:

Roderigo, if thou hast that in thee indeed, which I have greater reason to believe now than ever—I mean purpose, courage, and valour—this night show it. If thou the next night following enjoy not Desdemona, take me from this world with treachery, and devise engines for my life.

Roderigo falls for this ploy and agrees to show his courage by killing Cassio, playing into Iago's hands.

While Roderigo is a bit of a fool and shows a lack of moral compass, we should keep in mind that Iago is a master manipulator who everybody trusts. In other words, Roderigo may be less foolish than he looks: he is in the hands of a master sociopath.

Why is Iago determined to destroy Desdemona in Othello?

Othello's decision to choose Michael Cassio to serve as his lieutenant is the primary reason Iago seeks revenge. Iago believes that he is significantly more qualified than the young Florentine soldier and resents Othello for giving Cassio the esteemed title of lieutenant. Iago also wants to avenge Othello for sleeping with his wife, Emilia. Iago's racial slurs and derogatory remarks concerning Othello's race and ethnicity are additional motivating factors for him to seek revenge.

Iago also knows that Desdemona is the love of Othello's life and the person he adores the most. Iago desires to sleep with Desdemona in order to make things even, but Desdemona's loyalty to Othello makes this an impossibility. However, Iago reasons that it will be relatively easy to make Othello jealous and manipulate him into believing that Desdemona is sleeping with the younger, more attractive Michael Cassio. Since Iago cannot have Desdemona to himself, he is committed to destroying her happy marriage. Iago essentially uses Desdemona as a pawn in his scheme to ruin Othello. By convincing Othello that Desdemona is having an affair, Iago successfully ruins Othello's peace of mind and influences him to murder his beloved wife.

Why is Iago determined to destroy Desdemona in Othello?

In Shakespeare's Othello, Iago is committed to destroying Desdemona. He realizes this is the most effective way to get back at Othello. Iago hates Othello. Othello overlooked him and named Cassio as his lieutenant. Iago is determined to get revenge.

He is disgruntled at having been passed over for promotion, and he sees a chance to get back at both Othello, who has slighted him, and Cassio, the mocking symbol of that slight.

Iago creates an evil plan to accuse Desdemona of having an affair with Cassio. In this way, Iago can drive a stake in Othello's heart. Othello is madly in love with Desdemona. Iago knows this fact. He uses Othello's jealous emotions toward Desdemona to get back at Othello. 

Iago will stop at nothing to see Othello suffer. He knows that the best way to get back at Othello is through the love of his life, Desdemona. Also, Iago hates Othello for his suspicion that Othello has slept with Iago's wife Emilia. For this reason, Iago is determined to use Desdemona to destroy Othello:

 I do suspect the lusty Moor [Othello]
Hath leap'd into my seat; the thought whereof
Doth (like a poisonous mineral) gnaw my inwards;
And nothing can or shall content my soul
Till I am evened with him, wife for wife.
(II.i.299-303)

Iago is determined to destroy Othello so he sets Desdemona up. Also, Iago manipulates other people in the play to get what he wants. Iago's ultimate goal is to get revenge for Othello's choice of lieutenant and to pay Othello back for sleeping with his wife.

Iaga has a plan to have Roderigo kill Cassio. Iago is evil. He wants Cassio's position. He uses Desdemona as a part of his evil plan.

Iago recognizes that Desdemona is kind. He encourages Cassio to speak with Desdemona after Cassio loses his position as lieutenant. As a master manipulator, Iago twists the facts to further his evil plot. He whispers suggestions to Othello to make it appear that Desdemona and Cassio are having an affair. Because Othello idolizes his wife, he becomes jealous to a  point of rage.

Iago knows that Roderigo also loves Desdemona. He uses this fact to turn Roderigo against Cassio. Iago wants Cassio dead. He sets up Roderigo in a plan to get Roderigo to kill Cassio. Desdemona is at the center of Iago's plan. He uses the love Othello and Roderigo have for her to advance his plot.

Desdemona dies as a result of Iago's evil scheme. Iago is one of Shakespeare's most evil villains. He destroyed Desdemona along with Othello. Desdemona means nothing to Iago. Ultimately, Iago is bent on destroying Desdemona because Desdemona is the closest person to Othello.       

What quotes in Shakespeare's Othello portray Iago's betrayal of Othello?

Iago is depicted as the ultimate villain, carefully planning and executing an impressive plot to get revenge on Othello. He seeks revenge because Othello did not promote him to the revered position of lieutenant and gave the title to the inexperienced Michael Cassio. Iago also suspects that Othello has slept with his wife and proceeds to manipulate several characters in order to get revenge. Despite Iago's malevolent intentions, Othello completely trusts him and believes that he is a benevolent, loyal subject.

Iago's betrayal is poignantly depicted in act three, scene three, when he initially begins to plant the seeds of jealousy and suspicion into Othello's head. When Othello witnesses Cassio run away after speaking with Desdemona, Iago insinuates that Desdemona and Cassio are engaged in an affair and warns Othello about the dangers of jealousy. Iago proceeds to say,

I speak not yet of proof.
Look to your wife, observe her well with Cassio.
Wear your eyes thus, not jealous nor secure.
I would not have your free and noble nature
Out of self-bounty be abused. Look to ’t.
I know our country disposition well.
In Venice they do let God see the pranks
They dare not show their husbands.
Their best conscience
Is not to leave ’t undone, but keep’t unknown. (3.3.201-209)

Iago continues to betray Othello by painting Desdemona in a negative light and reminding him of how she cleverly deceived her father. Iago's portrayal of Desdemona raises concerns about her honesty, and Othello begins to entertain the idea of his wife's infidelity. Iago continues to play on Othello's insecurities by saying,

Ay, there’s the point. As, to be bold with you,
Not to affect many proposèd matches
Of her own clime, complexion, and degree,
Whereto we see in all things nature tends—
Foh! One may smell in such a will most rank,
Foul disproportions, thoughts unnatural.
But—pardon me—I do not in position
Distinctly speak of her, though I may fear
Her will, recoiling to her better judgment,
May fall to match you with her country forms,
And happily repent. (3.3.234-244)

Once Othello begins to doubt Desdemona's faithfulness, Iago leaves him with his tortured thoughts and receives Desdemona's handkerchief from Emilia. Iago proceeds to elaborate on the rest of his plan during an aside by saying,

I will in Cassio’s lodging lose this napkin
And let him find it. Trifles light as air
Are to the jealous confirmations strong
As proofs of holy writ. This may do something.
The Moor already changes with my poison. (3.3.331-335)

Overall, Iago's betrayal of Othello is depicted in act three, scene three, when he insinuates that Desdemona is having an affair with Cassio and manipulates Othello's insecurities. Othello becomes tainted by Iago's suggestions and becomes suspicious of his wife.

What quotes in Shakespeare's Othello portray Iago's betrayal of Othello?

A particular quotation from act 1, scene 3 is a great example of Iago's treachery:

Thus do I ever make my fool my purse,
For I mine own gained knowledge should profane
If I would time expend with such a snipe
But for my sport and profit.

Iago has just sent the hapless Roderigo off to sell his land. He told the foolish young man that he needed to do this in order to raise enough money to woo Desdemona, with whom Roderigo is head over heels in love. But in actual fact, the wicked, scheming Iago intends to cheat Roderigo out of his money. This is what he means when he says that he has made a fool his own purse.

It's at this point in the play that we realize just how wicked Iago really is. He will stop at nothing to get his own way, even if it means stealing from those ostensibly on the same side as himself. Iago is a user, a master manipulator with the ability to get other people to do his own bidding. And all the while they never know they're being duped until it's too late.

So will I turn her virtue into pitch
And out of her own goodness make the net
That shall enmesh them all.

These lines come from act 2, scene 3. Here, Iago is referring to his dastardly scheme to destroy Desdemona. He's going to trash her reputation, turning her virtue into pitch, which is a kind of black, sticky substance. He then mixes his metaphors by saying that he will make a net out her goodness that will trap everyone else he wants to destroy. Iago cleverly realizes that by destroying Desdemona's reputation for virtue, he'll also destroy his enemies with one fell swoop.

What quotes in Shakespeare's Othello portray Iago's betrayal of Othello?

Iago's betrayal is a central theme in Shakespeare's Othello, and, therefore, the play is full of lines portraying his betrayal. While we are limited to space, below are a few ideas of types of quotes to look for that help prove and demonstrate his betrayal.

One good type of quote to look for is anything relaying the reasons for his betrayal. Iago betrays Othello out of jealousy because Othello chose not to promote him to lieutenant, despite his merit, but instead chose another officer. Therefore, any quote explaining what Iago perceives as Othello's offense will help prove that Iago betrayed Othello by showing us the reasons why. For example, in his first speech, Iago argues that he knows he would be valuable as a lieutenant and should have been chosen:

I know my price, I am worth no worse a place.
But he, as loving his own pride and purposes
Evades them with a bombast circumstance
...
And, in conclusion, ... says he,
"I have already chosen my officer." (I.i.11-17)

The second type of quote would be any quote discussing Iago's plans for betrayal. In Act II, Iago observes Desdemona and Cassio flirting and concocts his plan to make Othello jealous. Not only that, he believes that Othello has slept with his own wife and therefore wants to avenge himself, not just for failing to promoting him to lieutenant but also for sleeping with Iago's wife, as we see him state:

And nothing can or shall content my soul
Till I am even'd with him, wife for wife;
Or failing so,, yet that I put the Moor
At least into a jealousy so strong
That judgement cannot cure. (II.i.306-310)

All of these types of lines will help convey and prove Iago's betrayal of Othello.  

How does Iago manipulate Othello?

At the beginning of the play, Iago divulges his vengeful and maliciously devious intention to manipulate and mislead Othello, his so-called friend. He tells Roderigo, "I follow him to serve my turn upon him." He means that he intends to mislead Othello by continuing to act as his trustworthy and obedient agent while, in fact, plotting against him.

Iago and Roderigo later successfully demonize Othello by convincing Brabantio that the general has abducted his beautiful daughter, Desdemona. Brabantio is driven to fury and decides to have Othello arrested for such an ignominy. At this point, Iago informs Roderigo that he has to leave and join Othello to further convince the general of his support. He tells Roderigo:

Yet, for necessity of present life,
I must show out a flag and sign of love,
Which is indeed but sign. 

Iago's action in this regard epitomizes the nature of his strategy, which is to convince the general of his total commitment. In this way, Iago will not only retain Othello's trust but also deepen his leader's belief in him. 

In scene 2, Iago tells Othello about his supposed anger at Brabantio for insulting the general and states that he could hardly bear listening to the senator's diatribe. To further confirm his loyalty, Iago later challenges Roderigo to a duel when the latter arrives in the company of Brabantio and others to accost Othello. Iago's attitude certainly convinces the general that his loyalty lies with him.     

In act 2, scene 3, Iago and Roderigo's plot to have Cassio demoted is successful when Othello dismisses the young lieutenant from his service. Iago advises the distraught soldier to sequester Desdemona's help for reinstatement. It is Iago's sly intent to use Cassio to further his malicious plan by cleverly intimating to Othello that Cassio and Desdemona are having an affair.

Iago's first opportunity to implicate Cassio occurs in scene 3 of act 3 when, upon seeing Cassio trying to slip away surreptitiously after consulting Desdemona, he remarks: "Ha! I like not that." On hearing the comment, Othello wishes to know what he has said. Iago feigns ignorance.      

When Othello asks whether he is correct in believing that he has just seen Cassio walking away from his wife, Iago replies that he cannot believe that it could have been Othello's ex-lieutenant who "would steal away so guilty-like, seeing you coming." Iago's careful diction is loaded with innuendo and suggests that Cassio has done something wrong. Othello is, of course, annoyed when Desdemona later tells him that she has been speaking to Cassio.       

Iago has now cunningly baited Othello and proceeds to prey on the general's insecurities through further insinuation. He picks Othello's mind and provides him little bits of perfidious information by asking about Cassio's previous associations with  Desdemona. Furthermore, he plays on the general's mind by being evasive. Iago drives Othello to suspicion by suggesting that there is something untoward about Cassio's relationship with Desdemona.

Receive it from me. I speak not yet of proof.
Look to your wife; observe her well with Cassio;
Wear your eye thus, not jealous nor secure:

He also preys on the general's ignorance about Venetian customs and hints that Venetian wives are wont to have secret adulterous affairs. By deliberately speaking about jealousy, Iago is, in fact, encouraging the general to be jealous.

At the end of act 3, scene 3, Iago tells Othello a blatant lie by mentioning an incident in which Cassio supposedly declared his passion for Desdemona. He states that he and Cassio had been sharing a bed when the soldier, while having a dream, attempted to mount him, mentioning Desdemona's name. Iago's coup de grace comes in the form of Desdemona's handkerchief which his wife, Emilia, gives to him. He plants it in Cassio's room and later uses it as proof of Desdemona and Cassio's iniquity. He tells the general that he has seen Cassio wipe his beard with it.

Othello is so overwhelmed that he vows to take revenge on both his wife and Cassio. Iago uses the opportunity to show his purportedly unquestionable allegiance and kneels. He swears to do whatever his general commands. Othello asks him to kill Cassio within three days while he takes care of Desdemona. He then names Iago his lieutenant.

In act 4, scene 1, in his final act of supreme manipulation, Iago manages to convince Othello that Cassio is speaking about Desdemona while the general eavesdrops on his and Cassio's conversation about Bianca, a prostitute who is in love with Cassio. Cassio speaks about Bianca disdainfully. 

When Bianca arrives later, Othello is even more convinced when she expresses anger at Cassio for having dared to ask her to work on a handkerchief (Desdemona's) which he had given her. Othello has now had his "ocular proof." In his later conversation with Iago, he promises to chop Desdemona "into messes" or poison her, but he is persuaded by his lieutenant to strangle her in her bed. 

Iago's manipulation culminates in the tragedy which sees Desdemona, Emilia, Roderigo, and Othello die.

How does Iago manipulate Othello?

Act 3 Scene 3 is known as “the seduction scene” (or “the manipulation scene”) because here Iago tricks Othello into believing that Desdemona is having a love affair with Cassio.  Iago and Othello enter just before Cassio leaves, hearing the tail-end of the conversation. Iago says, “Ha! I like not that.,”  which triggers a back and forth repartee between Iago and Othello that is like a dance:  Iago drops a hint or uses a tone suggesting a relationship between Desdemona and Cassio, Othello asks what he means by the comment, Iago then demurs, only for Othello to demand more information, seemingly dragging it out of Iago while all the while it is Iago leading this dance.  Iago’s skills at manipulation result in tremendous irony, for we the audience know what Iago is up to, but Othello seems like a dupe in not understanding what seems to us obvious manipulation.

How does Iago manipulate Cassio differently than Roderigo and Othello?

Iago is the spider who weaves his web that will "ensnare them all."  But the methods Iago uses for each of these three characters are indicative of their intellect, integrity, and passions.  For Roderigo, Iago appeals to his sexual desire to obtain Desdemona for his own.  Roderigo is easily manipulated.  All Iago has to do is mention Desdemona as bait, and Roderigo will do whatever Iago asks:  sell his lands, give Iago more money, follow Iago to Cyprus, pick a fight with Cassio.  Iago's main method of persuasion with Roderigo is repetition:  "Put money in thy purse," Iago tells Roderigo over and over again.

Cassio is more of a challenge for Iago.  Cassio is a courtier with good looks, fine manners, and a good education.  Cassio's weakness is that he cannot hold his licquor.  So, Iago gets him drunk, and sends Roderigo to pick a fight with him.  This fight has consequences beyond Iago's wildest dreams, ending with Cassio wounding Montano and losing his position as lieutenant.  This fight took some maneuvering, but Iago was quite successful in bringing Cassio down.  The second part of his plan, to make Cassio seem like Desdemona's lover, required much cleverness.  When Cassio turns to him for advice, Iago tells him to go to Desdemona to get his position back, and Iago will, of course, make this innocent conversation seem like something else.  If Cassio were not the conscientious soldier that he is, or if Cassio had been unwilling to accept the responsibility of his own drunken actions, or if Cassio had been less loyal to Othello, Iago's plan would not have worked.  Cassio is indeed a "great fly," caught in Iago's net.

With Othello, Iago must pull out all the stops.  Othello is much more difficult to manipulate than either Roderigo or Cassio.  Othello is powerful, honorable, deeply in love, "not easily made jealous."  Iago resorts to suggestion, innuendo, reverse psychology, staging, oaths of loyalty, "ocular proof" (the handkerchief), racial and gender stereotyping.   Iago's manipulation of Othello comprises most of Act 3 and part of Act 4.  Othello does not fall easily, demanding that Iago "prove his love a whore."  In this way, Othello is clearly a more complex and intriguing character than Cassio or Roderigo. 

In Othello, why does Iago want to destroy Othello, Desdemona, and Cassio—despite the fact that he already got Cassio fired?

This is, without hyperbole, one of the most written upon character-based questions in Western literature. There have already been a couple good answers on here about Iago’s anger that he was passed up for promotion.

His line early in the play: “I hate the moor,” also suggests a possible undercurrent of racist motivation. (A quick side note: Othello is meant as a dark Turkish character, but in Shakespeare’s time might not necessarily have been represented as “black” the way the part is today. Though it also very likely could have been played in blackface. Either way, the racist undertones persist.) Iago also states that he suspects Othello might have slept with his wife Emilia, though how deeply he believes this suspicion is open to debate.

Iago’s true motivation is a difficult question to answer. One of the fascinating things about his character is that he gives so many different reasons to hate Othello (listed above), yet scholars still feel sure there must be some deeper, grander root of his evil. The moment that separates Iago from the rest of the villains in Shakespeare’s canon, and indeed makes him the best of Shakespearian villains, is his own explanation of his misdeeds after he’s found out and captured:

Demand me nothing. What you know, you know.
From this time forth I never will speak word.

These are chilling last lines from a character who spent the majority of the play strategizing and using others as puppets. Scholarship might debate the question of Iago’s intentions for another four hundred years. But the mystery of his evil and his refusal to speak on them is more than a literary puzzle. The mystery of Iago’s intentions is one of the most engaging aspects of his character and is part of why he has endured as one of the best literary villains of all time.

In Othello, why does Iago want to destroy Othello, Desdemona, and Cassio—despite the fact that he already got Cassio fired?

Iago particularly wants to destroy Othello to seek revenge for Othello's naming Cassio as lieutenant.  Iago felt certain that Othello would give the title to him, so when Othello names Cassio instead, Iago is full of rage.  Further, Iago thus becomes jealous of Cassio because he is now of a higher rank and is young and handsome to boot.  Desdemona gets wrapped into Iago's evil plotting by mere circumstance--Iago knows that Othello values Desdemona and their relationship above all else, so Iago uses Desdemona as a tool in his plan. 

Iago becomes overtaken by his own jealousy and rage, so he continues with his plans even after Cassio is fired.  By this point in the play, Iago is no longer trying to get the rank--he is almost obsessed with seeing Othello's fall.

In Othello, why does Iago have a strong influence on Othello?

I'd say there's three main reasons:

1) Clever psychological manipulation. Iago knows exactly what to suggest, and when to suggest it. He says things briefly, succintly - those four devastating words "look to your wife" start a whole battery of thoughts in Othello's mind. He also (note the way he makes Othello force him to keep speaking, by making a suggestion and then dropping it) makes Othello demand to know things from him - allowing him to seem more honest and innocent. And because Othello thinks him honest, Iago can easily lie to him.

2) Othello's own insecurities. Othello makes a telling speech after Iago has exited, about why Desdemona might have cheated on him:

Haply, for I am black
And have not those soft parts of conversation
That chamberers have, or for I am declined
Into the vale of years—yet that's not much—
She's gone. I am abused, and my relief
Must be to loathe her.

Othello is a foreigner (note that Iago emphasises that he knows all about Venetian woman - implying that Othello doesn't), he is racially different, and he is older. He feels insecure, I'd argue, about each of this things, and Iago's suggestions activate that insecurity, which in turn defeats his better judgement.

3) Good luck. Iago does seem to have ideas and plans, but some crucial turns - Cassio getting as drunk as he does, Desdemona dropping the hankerchief - are just down to good fortune.

Hope it helps!

In Othello, why does Iago have a strong influence on Othello?

Iago is one of the most nefarious villains in all of Shakespeare because he seems to delight in his own selfish revenge and loves to do evil for evil's sake. Iago completely manipulates Othello because he manipulates situations, other characters, and even what Othello sees and hears.

Othello is a play of psychological manipulation. Iago first manipulates Cassio's watch so that Cassio's reputaion is erroded and his is "plumed up" in the process. Having disposed of Cassio's reputation in this way, he is free to change the Moor's passionate disposition by whispering such things as "I like not that" when Cassio and Desdemona are together. By "pouring poison" into the Moor's ear and letting O's imagination do its worst, is Othello completely ensnared.  

Iago manipulates the Moor by orchestrating a discussion Iago has with Cassio where C talks of Bianca (but O thinks it's Desdemona), provides "ocular proof" of Desdemona's supposed infidelity, and pretends to be Othello's "blood" brother. In orchestrating the chance encounters, other characters' actions and speech, and through a manipulation of the passionate General himself is Iago able to "completely" influence Othello, 

What should be Iago's punishment in Othello?

Until the last act of Shakespeare's Othello, Iago hasn't actually committed any crimes other than to manipulate others to the his "dirty work" and persuaded Othello into thinking the Desdemona was unfaithful to him and drive him into a jealous rage against her.

In act 5, scene 1, Iago's plans start to unravel, and he wounds Cassio and kills Roderigo.

In act 5, scene 2, after Othello kills Desdemona, Iago's wife, Emilia, reveals that Iago is responsible for all of the death and destruction that he instigated throughout the play. Iago becomes incensed at Emilia, stabs her, and runs off. Emilia dies a short time later.

Iago is apprehended and brought back to Othello and the others assembled with him, and Othello stabs Iago but doesn't kill him.

Under English law during Shakespeare's time, Iago would be hanged for the murders of Roderigo and Emelia. Othello isn't set in England, however, so English law doesn't apply to the crimes that are committed during the play. The first act of Othello takes place in Venice, and the balance of the play is set in Cyprus. The murders of Roderigo, Emilia, and Desdemona occur in Cyprus and therefore would seem to be subject to the laws of Cyprus.

Othello is set against at the time of the wars between Venice and Turkey in the latter part of the sixteenth century. Cyprus was actually attacked by the Turks in 1570, and in the play, Othello is sent to Cyprus to fortify Cyprus's defenses and prepare for an attack from the "Ottomites," another word for Turks.

Research into the Cypriot laws in effect in the late 1500s regarding the penalty for murder would seem to be a good place to start for information about Iago's punishment for his crimes.

Another thing to consider is that after Iago kills Emilia, he refuses to answer any questions or to speak further about anything he's done. Gratiano suggests that torture might get Iago to talk.

IAGO. Demand me nothing; what you know: you know.
From this time forth I never will speak word.

LODOVICO. What, not to pray?

GRATIANO. Torments will ope your lips. (5.2.347-350)

In the last lines of the play, Lodovico, too, calls for Iago's torture.

LUDOVICO. To you, Lord Governor,
Remains the censure of this hellish villain,
The time, the place, the torture. O, enforce it! (5.2.418-420)

This opens up another line of research as to whether torture was appropriate under the law for Iago's crimes, and whether torture should be included in Iago's punishment.

What should be Iago's punishment in Othello?

You could begin with a brief overview of the plot. Background information is necessary. You are to assume the reader may not know the background information of the play Othello. 

Your thesis could be that Iago deserves punishment by death. You could write about the reasons Iago deserves punishment by death. After all, he was responsible for the death of Roderigo. He is responsible for the death of Desdemona. He is responsible for the death of his own wife Emilia. How could anyone expect Iago to escape death himself. Iago was an evil character and he deserves punishment by death. 

The death penalty is for evil people and Iago fits the definition. He manipulated so many in the play. He cared only about himself. He caused two people who loved each other dearly to lose their marriage--Othello and Desdemona. 

Iago destroyed life after life to gain self satisfaction. He was cruel and heartless. Punishment by death is befitting for Iago. If he were to stand trial today, no doubt he would receive the death penalty. 

Iago remains to be one of Shakespeare's most evil characters and he deserves the death penalty:

Regardless of the degree to which Iago is to blame for Othello's downfall, he remains one of Shakespeare's most villainous creations, variously described as a brilliant opportunist taking advantage of the chances presented to him, as a personification of evil, and as a stock "devil" or "vice" figure.

How does Shakespeare present manipulation through Iago in Othello?

Iago is the master manipulator. His manipulations work because people trust him.

Shakespeare presents Iago as the kind of person who performs character assassination through insinuation. He drops a hint that something is wrong; then, when he is pressed, he protests he didn't mean to say anything or that he likes the person in question too much to want to say what he knows. Then, when he is pressed to tell, he lets the curious person drag a lie out of him, as if he is unwilling to betray anyone.

He does this with Othello, pretending that the last thing he wants he to do is to implicate Cassio as Desdemona's lover. Only when Othello insists does Iago tell the lie that, while dreaming, Cassio mistook Iago for Desdemona, flung his leg over Iago's thigh and kissed Iago on the mouth while murmuring that he wished Othello was dead. All of this is an utter fabrication, but it manipulates Othello into a frenzy of jealousy, which was entirely Iago's intention.

It's worth noting that Shakespeare also uses dramatic irony to present Iago's manipulations. Iago is always telling the audience what is really on his mind, so we know what he is doing to innocent people and can only watch in horror as they are duped. It would be interesting to think about how the play would unfold were we not privy to Iago's twisted secrets: would we be just as deceived as the characters?

How does Iago use his power of persuasion with Roderigo, Brabantio and Othello?

Iago has a persuasive tongue and knows how to emotionally manipulate people. He has an easy time with Roderigo, who is a fool. Roderigo tells Iago he is so upset that Othello married his beloved Desdemona that he wants to drown himself. Iago tells him that romantic love is a ridiculous illusion and only to drown kittens. He manipulates Roderigo by telling him to look instead to the future. He says that Desdemona will soon tire of Othello, so Roderigo should save his money to be able to woo her with jewels and fine gifts. Iago says:

It cannot be that Desdemona should long continue her
love to the Moor—put money in thy purse . . .

When Roderigo gives money to Iago to buy jewels, the money—surprise!—disappears.

Iago does his best to persuade Roderigo to his own sordid view that love is no more than carnal desire and that Roderigo should go after it any way he can, stating:

if thou canst cuckold him, thou dost
thyself a pleasure, me a sport.

With Brabantio, Desdemona's father, Iago uses crude language of a black ewe tupping (having sex with) a white lamb to try to put visual images into Brabantio's mind of an animal despoiling his pure daughter. He wants to incite Brabantio's rage so that he will have the marriage annulled—and he succeeds for a time in enraging Brabantio, until Desdemona is able to persuade her father she really does love Othello.

Iago uses the same technique to try to inflame Othello and turn him against Desdemona. He does his best to get Othello to picture the Desdemona and Cassio in bed together having sex. He uses lies and innuendo, as well as the technique of pretending not to want to say—always after dropping hints to make Othello curious. He does manage to set Othello against his wife, with tragic results.

How does Iago exploit Othello's character to achieve his own end?

Iago exploits many aspects of Othello's character to achieve his own end--making those around him as miserable as he is.

Some characteristics you might consider are the following:

(1)  Othello is trusting:  "He thinks men honest that but seem to be so."  Othello is a good man, and because he is honest and forthright, he sees others in this way.  Iago knows that Othello thinks he (Iago) is honest, and that he trusts Iago's knowledge of people.

(2) Othello is a soldier, a man of action, one who must make decisions quickly.  As a soldier, he would view betrayal as one of the worst offenses.  And as acting head of Cyprus, Othello would view betrayal as an act of treason.  We see Iago using this characteristic when he tells Othello to let Desdemona live.  This type of reverse psychology works just the way Iago had planned, making Othello even more determined to kill her.

(3) Othello  is also a man of absolutes.  He either loves or he hates.  He is not lukewarm.  As he says about himself:  "Away at once with love or jealousy."  Othello's definition of love requires absolute trust.  He cannot simultaneously love and be jealous or suspicious.  So, Iago knows that if he can plant any doubt in Othello's mind about Desdemona's infidelity, he will succeed.

(4) Othello is somewhat insecure about matters of the heart.  While he is excellent as a military man, in domestic matters he is somewhat ill at ease.  Even in act one, Othello apologizes for his speech:  "Rude am I in speech and have not those soft parts of conversation that chamberers have."  Iago points out that Cassio is young, a courtier, "framed to make women false"  -- in many ways Othello's opposite.

How does Iago manipulate Cassio after the lieutenant's humiliating dismissal?

After he is dismissed from his position as Othello's lieutenant, Cassio is primarily concerned with his newly-tarnished reputation.  Iago, recognizing Cassio's vulnerability and desperation to win back Othello's favor, decides to council Cassio regarding the best way to reconcile with the general.

Iago's advice, when taken at face value, is good; he advises Cassio to seek Desdemona's help, observing that she always goes above and beyond to help someone who asks her to do so:

She is so free, so kind, so apt so

Blessed a disposition, she holds it a vice in her goodness

Not to do more than is requested.

Iago further describes the influence Desdemona has on Othello, and assures Cassio that all will be well if he follows Iago's suggestions.

At the same time, though, Iago plans to tell Othello that Cassio is "too familiar" with Desdemona--an accusation that he knows will inevitably drive Othello into a fit of jealousy.  At the end of Act 2, Iago justifies his actions in a soliloquy:

And what's he then that says I play the villain?

When this advice is free I give and honest,

Probal to thinking, and indeed the course

To win the Moor again?

Ultimately, Iago's plan is clearly a manipulation of Cassio--as well as the other characters involved.

How does Iago arouse Othello's suspicion in the conversation between Cassio and Desdemona?

How hard it is to convince a rock that it is hard?  Or water that it is wet?  Or a green-eyed monster that it is green?  Or monstrous?

In Othello, Iago's plan to arouse Othello's jealousy is simple and easy.  All he has to do is make an accusation: Othello will take care of the rest.

So says author and critic Salman Rushide:

She [Desdemona] didn't have to be guilty; the accusation was enough. The attack on her virtue was incompatible with Othello's honor.

Iago knows that Othello is paranoid of being thought a cuckold, a man whose wife lays her eggs in other birds' nests.  It is the worst thing to call a man back then--worse than any racial epithet.  In this sexist society, it is not difficult to portray women as unfaithful in a society where men think women are all unfaithful.  It's not difficult to convince a man of jealousy when his is already jealous.  It's not difficult to convince of husband that his wife is flirting when the husband is paranoid about it already.

Here's all Iago has to say:

Look to your wife; observe her well with Cassio;
Wear your eye thus, not jealous nor secure:
I would not have your free and noble nature,
Out of self-bounty, be abused; look to't:
I know our country disposition well;
In Venice they do let heaven see the pranks
They dare not show their husbands; their best conscience
Is not to leave't undone, but keep't unknown.

Iago's imagery is clearly visual: "look" and "observe."  Men are arrogant enough to think they can read women's minds. And the Venetian society is built on distrust of women!  All Desdemona has to do is laugh at Cassio's jokes, or touch his hand: Othello's jealousy is inevitable.  The "green-eyed monster" isn't born in Act II or III--it has always been in Othello and other men of that time too.

Explain how Iago is manipulative by how he persuades Othello to kill Desdemona. Include significant quotations and examples of this.

Because Iago is very good at being deceptive, he convinces Othello that his wife has been unfaithful with Cassio. Truly, Iago is a intelligent, gifted man. He understands what motivates the characters he manipulates.   

Because Othello and Iago have been warriors, side-by-side, Othello trusts Iago:   

Iago is a soldier with a good deal of experience in battle, having been on the field with Othello at both Rhodes and Cyprus. 

No doubt, Iago considers Othello, the Moor, as a man who can easily be fooled and led around as one would lead an ass:

The Moor is of a free and open nature,
That thinks men are honest that only seem to be so;
And will as tenderly be led by the nose
As asses are.

Truly, Iago is sure of himself. Iago begins his evil plot by planting seeds of jealousy in othello. 

To further his evil plot, Iago brings up the fact that Desdemona has been dishonest before. Iago reminds Othello that Desdemona lied to her father in the beginning. He reminds Othello that Desdemona did not tell her father the truth about her marriage to Othello:

She deceived her father by marrying you;

When Othello thinks about Iago's accusation that Desdemona was dishonest with her own father, Othello begins to suspect that Desdemona may be dishonest in other areas of her life. Iago plants seeds of doubt in Othello's mind and heart. Othello is afraid that Desdemona may lie about other things as well as she lied to her father about her secret marriage to Othello. 

Of course, Iago quickly assures Othello that he did not mean to upset him. He realizes that Othello is clearly upset at the thought of his precious Desdemona being capable of lying. Iago realizes that his plan is working. To protect himself, Iago reminds Othello that he truly loves him. Iago is an excellent actor:

My lord, you know I love you.

Then Iago continues to assure Othello that he only created suspicion about Desdemona due to his true love for Othello:

I hope you will consider that what I have spoken
Comes from my love; but I see you're upset.

Othello believes every word Iago says. Othello thinks Iago is very honest and trustworthy: 

Othello calls him honest, honest Iago (V.ii.155),

This why Othello turns against his beloved Desdemona. Also, Othello has self-esteem issues. He feels that he is much older than Desdemona. He also mentions that his skin color, which is black, may have a negative effect on his lovely wife. Truly, Othello is not secure in his position as Desdemona's husband. He doubts that she could love him for various reasons:

Maybe, because I am black,
And don’t have those soft parts of conversation
That gentlemen have; or because I am getting
Much older, still that's not much,
She's already unfaithful; I am abused, and my relief
Must be to hate her. O curses on marriage,

Iago plays on Othello's low self esteem. He uses Othello's lack of confidence to further convince him that Desdemona has been unfaithful to him. Iago is crafty, sly, and very tenacious. Iago is a clever, cunning manipulator. He knows Othello's weaknesses and he uses this knowledge as an advantage over Othello.

Clearly, Iago plays Othello for a fool. Ultimately, Othello murders his beautiful, innocent wife. Iago wins.

In the end, Emilia convinces Othello that Iago has been behind the whole evil plot of destroying Othello's marriage. When Othello learns the truth about Iago, he realizes he has smothered his innocent, loving wife. Othello cannot live with himself. He stabs himself, thus committing suicide.  

How does Iago instigate and amplify the idea of Desdemona's infidelity in Othello's mind?

Act 3, Scene 3 is the fateful moment in the play when Iago plants the first seeds of suspicion in Othello's mind. As always, Iago is remarkably subtle, using sly hints and innuendo to carry out his foul deed. At the beginning of the scene, Cassio is in conversation with Desdemona, hoping that she will intercede with her husband on his behalf to get him reinstated as Lieutenant.

Iago and Othello suddenly enter; Cassio hurriedly departs. It all looks rather suspicious, even though there is absolutely nothing going on between Cassio and Desdemona. There is a perfectly valid reason for Cassio's haste: he is still embarrassed about his drunken antics the night before. Nevertheless, Iago immediately spies his opportunity and takes it:

IAGO

Ha! I like not that.

OTHELLO

What dost thou say?

IAGO

Nothing, my lord: or if—I know not what.

OTHELLO

Was not that Cassio parted from my wife?

IAGO

Cassio, my lord! No, sure, I cannot think it,
That he would steal away so guilty-like,
Seeing you coming.

OTHELLO

I do believe 'twas he.

Notice how Iago explicitly says that he does not think that Cassio would leave "so guilty-like." Yet, at the same time, he is deliberating establishing a link between Cassio and the word "guilty," immediately sowing more than a hint of suspicion in Othello's mind. Iago's evil ploy appears to bear fruit almost at once. Othello starts acting abruptly toward Desdemona when she asks him when he might accede to Cassio's request:

Prithee, no more; let him come when he will, / I will deny thee nothing.

When they are alone together, Iago asks Othello further leading questions about Cassio, designed to fan the flames of jealousy further. Sensing Othello's growing suspicion, Iago takes things up a notch:

Good my lord, pardon me:
Though I am bound to every act of duty,
I am not bound to that all slaves are free to.
Utter my thoughts? Why, say they are vile and false;
As where's that palace whereinto foul things
Sometimes intrude not? who has a breast so pure,
But some uncleanly apprehensions
Keep leets and law-days and in session sit
With meditations lawful?

Again, Iago is using innuendo to manipulate Othello. He is implying that he has negative thoughts about Cassio, but he dare not let on what they are. He knows that Othello will compel him to reveal what he claims to know about Cassio. Othello pretends to be unconcerned, but Iago knows that is not the truth. In order to seal the deal, Iago needs some hard evidence. There is not any, of course, so he makes it up. His wife, Emilia, picks up Desdemona's dropped handkerchief, a love token from Othello, and gives it to Iago. He then plants it on Cassio to "prove" that Desdemona gave him Othello's precious gift.

By the end of act 3, Othello has completely renounced his love for Desdemona, and Iago has managed to exert complete control over him. Desdemona's days are numbered.

In Othello, how does Shakespeare show the manipulation of Roderigo by Iago?

Shakespeare uses various instances throughout the play to illustrate Iago's malice and how easy it is for him to maneuver Roderigo into doing his bidding. We learn from the outset that Iago has some control over Roderigo, especially his money, for Roderigo tells him in Act I, scene 1:

...I take it much unkindly
That thou, Iago, who hast had my purse
As if the strings were thine, shouldst know of this.

Through their conversation, we discover that Iago is deeply embittered about the fact that his general, Othello, has appointed an outsider, Cassio, as his lieutenant instead of extending the honor to him, who has been his loyal and trusted servant. He has embraced Roderigo as a friend, more like a puppet, to assist him in avenging his humiliation for Othello's snub. The two are planning to sully the general's name and the idea is to awaken Brabantio, a senator, and inform him that Othello has abducted his daughter, Desdemona, and is at that very moment abusing her.

Iago hopes that this will result in Othello's dismissal and possible imprisonment, which will be an immensely gratifying situation to him. At the same time, he has convinced Roderigo that he will also profit from this malicious venture. Brabantio's address to Roderigo makes it clear that he had been attempting to woo the beautiful Desdemona but has been banished by Brabantio from his house and denied any contact with her. Roderigo is obviously infatuated with her.

We later learn that Iago has been using Roderigo's desire for Desdemona to manipulate the foolish young man, who seems to have more money than common sense. When their plot to have Othello shamed fails hopelessly because Desdemona has come to his defense and expressed her love for him, Roderigo is wholly distraught since Othello was to leave Venice and travel to Cyprus with her. Not only has he lost the chance of wooing her, but she will also be gone—a reality that the lovesick fool cannot bear. He tells Iago that he will commit suicide.

Iago dismisses Roderigo's threat that he will drown himself as a preposterous notion. He urges him to fill his purse with money (at least eight times) so that he may win Desdemona's hand. He tells Roderigo, in part, the following:

...It
cannot be that Desdemona should long continue her
love to the Moor,

...nor he
his to her: it was a violent commencement, and thou
shalt see an answerable sequestration:

These Moors are changeable in
their wills: ... —the food
that to him now is as luscious as locusts, shall be
to him shortly as bitter as coloquintida. She must
change for youth: when she is sated with his body,
she will find the error of her choice: she must
have change, she must: 

if sanctimony and a frail vow betwixt
an erring barbarian and a supersubtle Venetian not
too hard for my wits and all the tribe of hell, thou
shalt enjoy her;

Roderigo seeks Iago's assurance that he will hold good his promise to, as it were, deliver Desdemona to him. Iago says:

Thou art sure of me:—go, make money:—I have told
thee often, and I re-tell thee again and again, I
hate the Moor: my cause is hearted; thine hath no
less reason. Let us be conjunctive in our revenge
against him: if thou canst cuckold him, thou dost
thyself a pleasure, me a sport. There are many
events in the womb of time which will be delivered...

This is the foundation on which Iago's manipulation of Roderigo rests. He promises the desperately infatuated wreck that he will ensure success in his desire to win Desdemona's hand. All that Roderigo has to do is to provide him with money. He should also travel to Cyprus in disguise, where the two of them will plot Othello's cuckolding. Roderigo will have Desdemona and Iago his revenge. Roderigo then sets off to sell all his land and Iago states:

Thus do I ever make my fool my purse:
For I mine own gain'd knowledge should profane,
If I would time expend with such a snipe.
But for my sport and profit.

Roderigo is a mere plaything in his hands, there for his pleasure, and he intends to get rid of him later.

Iago's manipulation of Roderigo continues later in the play. He informs Roderigo that Cassio and Desdemona are having an illicit affair and that he should be removed. When Roderigo expresses doubt about his assertions regarding Desdemona's virtue, Iago tells him that she is driven by lust and that Cassio is a lecher. He asks him to draw out and anger Cassio, so that he may be dismissed.

...So
shall you have a shorter journey to your desires by
the means I shall then have to prefer them; and the
impediment most profitably removed, without the
which there were no expectation of our prosperity.

The two men succeed in this enterprise and Cassio loses his post. Roderigo, however, loses patience and has no money and wants to return to Venice. Iago tells him to be patient. He later confronts Iago, stating that he feels that he is playing him for a fool. He threatens to approach Desdemona and expose Iago's malice. Iago, however, charms the blustering clod and informs him of a new plan: Othello would be leaving for Mauritania and Cassius would be appointed in his post in Cyprus. Desdemona will leave with Othello, removing her even further from Roderigo. To prevent this from happening, they need to get rid of Cassio. The gullible Roderigo once again takes the bait and promises to assist Iago.

When Roderigo confronts Iago and threatens to expose his scheme, he essentially signs his own death warrant, for, later, after the altercation with Cassio in which the erstwhile lieutenant and Roderigo are both injured, Iago surreptitiously appears and kills Roderigo, thus removing the threat. Later, though, a letter implicating Iago is found on Roderigo's person, which, with Emilia's accusation, leads to his arrest, incarceration and torture.

How does Iago control events in Othello?

Iago is the puppeteer; the other characters are his puppets.  He pulls the strings; the other characters dance to his music. He enrages Brabantio with his coarse language about Desdemona's elopement to Othello.   He manipulates Roderigo, getting him to sell all his lands:  "thus do I ever make my fool my purse."  He convinces Roderigo that he can have Desdemona if he will give Iago more money to gain her affections.  He uses peer pressure to get Cassio who has "poor and unhappy brains for drinking" to get so drunk that he injures Montano.  He persuades Cassio to go to Desdemona to regain his position as lieutenant.  And last, but most importantly, he convinces Othello that Desdemona is cheating on him and leads him to the conclusion that she and Cassio must be executed.

That said, Iago's powers are limited, and the characters allow themselves to be pawns.  Iago appeals to their dark sides; the characters have responsibility for their fates.  Brabantio might have trusted his daughter's judgment and respected her choice of a husband.  Roderigo, if he truly loved Desdemona, would not have interfered in her marriage.  Cassio knew he was not capable of holding his liquor and should not have allowed himself to drink, while he was on duty.  Othello, of course, should have trusted his wife.

Iago's machinations throughout the play are masterful.  Even Othello cries out at the end of the play, wondering why this "demi-devil... hath ensnared my soul and body."  Yet, the characters are not complete victims of his design.  They make choices that ultimately lead to tragedy.

How does Iago trick Othello into thinking Cassio was gloating and bragging about his affair with Desdemona?

It's important to note that at this point in the play, Othello is a frothing, jealous madman who is already convinced of Cassio and Desdemona's infidelity and has already sworn to punish them both for it.  So, at this point, Iago is really just taunting him further to make Othello even crazier.

Othello hides, and Iago carefully starts a conversation about Bianca with Cassio.  Bianca is a courtesan/prostitute that Cassio had taken up with.  Not having any idea of Iago's machinations, Cassio laughs uproariously and vulgarly talks about sleeping with Bianca, even making gestures.  Needless to say, Othello thinks Cassio is talking about Desdemona.

What methods does Iago use in Othello and why are they effective?

Iago's methods are devious, despicable, cunning, and utterly mendacious. They are also highly effective. Iago has the advantage over his adversaries in that he's so completely unscrupulous that he'll do anything and say anything to get what he wants. No one else in the play has ever encountered such a dark vision of wickedness before. But though very much the archetypal villain, Iago possesses in abundance the quality of dissimulation, the ability to conceal one's true thoughts and motives. The real Iago—hateful, vicious, and bitter—comes out in his soliloquies. But to those he wishes to destroy, he comes across as a perfectly charming, decent kind of chap, certainly not someone capable of stooping to such extraordinary depths of evil.

Iago is also remarkably flexible in his methods, skillfully adapting them to the person he wishes to manipulate. He is truly a psychologist of genius with a deep understanding of what makes people tick: of their fears, wishes, and desires. He has an unerring knack of identifying a person's weak spot and honing right in to exploit it to his advantage.

For instance, he plays upon his wife Emilia's love and dogged loyalty, getting her to steal Desdemona's handkerchief as part of his sinister plot to destroy her. With the callow young rake Roderigo, he acts the part of Dutch uncle, fooling him into believing that the delectable Desdemona is well within his grasp. And then of course there's Othello, Iago's nominal master. As a deeply insecure man himself, Iago understands all too well what it means to feel as if you don't fit in. Like the Moor, he's an outsider among the social elite of Venice. By slowly drip-feeding poisonous innuendo and insinuation into Othello's unsettled mind, Iago's able to convince him of Desdemona's infidelity despite a complete absence of corroborating evidence.

How is Iago able to manipulate Othello?Meaning, how does Iago bring him down in Othello?

Part of how Iago is able to manipulate Othello, and most others in the play, is his complete understanding of internal motivation and understanding of others.  Iago reads and understands many of the characters in the play rather well.  He knows very well where Othello's internal weaknesses lie and he is able to exploit them in manipulating Othello into doing what he wants him to do.  The notion of jealousy that lies inside Othello is something that Iago uses to bring down the mighty warrior.  Understanding that this might be due to the fact that Othello is an outsider, of a different religion, and of a different ethnicity, Iago is able to identify that Othello, for all his greatness, is extremely scared and insecure about losing everything.  Reading this well, Iago is able to understand that this doubt is what lies at the heart of all of Othello's success.  Striking at it in different ways is what allows Othello to be manipulated.

In Othello, elaborate how Iago manipulates other characters and achieve his goal?

Iago always uses the characteristics of his foes against them.  In the case of Othello, clearly his biggest goal of manipulation, he finds a way to use his confidence and his "warlike" abilities against him.  Having ended up on Cyprus and without a foe, Othello loses his great confidence in his abilities as a soldier and a general.

By using the fact that Othello is not as confident in his ability to actually win the heart of Desdemona, Iago prey's on Othello's insecurities.  He knows that Cassio is the darling of the royalty in Venice and so he would be the likely opponent in the contest for Desdemona, also royalty whereas Othello is an outsider and a moor.

What happens when Iago uses fallacy to manipulate others against Othello?

Shakespeare's Othello opens with Othello's ensign, Iago, remarking on his hatred of Othello and manipulating Roderigo, a former suitor of Iago's wife, Desdemona, into provoking Desdemona's father to denounce Othello to the Duke of Verona and his council of Senators for using witchcraft to trick Desdemona into marrying him.

Iago also plants the seed of further plots against Cassio, who is newly chosen by Othello as his lieutenant over Iago, who seethes in anger and jealousy toward Cassio.

IAGO. And what was he?
Forsooth, a great arithmetician,
One Michael Cassio, a Florentine
A fellow almost damn'd in a fair wife
That never set a squadron in the field,
Nor the division of a battle knows
More than a spinster;
... mere prattle without practice,
Is all his soldiership.
(act 1, scene 1, lines 18–27)

Othello is brought before the Duke, but Iago's plot to have Othello demoted and denounced fails.

Iago is undeterred. He decides to use Cassio in a plot against Othello in order to effect his revenge against both men.

IAGO. Cassio's a proper man. Let me see now:
To get his place, and to plume up my will
In double knavery—How, how?—Let's see—
After some time, to abuse Othello's ear
That he is too familiar with his wife.
(act 1, scene 3, lines 402–406)

This plot against Othello involving Cassio and Desdemona is the focal point of the play from this point forward.

Iago discovers that Othello is highly prone to jealousy, "the green-eyed monster," and by suggestion, innuendo, and circumstances involving Cassio and Desdemona and staged encounters with Cassio, Iago inflames Othello's jealousy into a murderous rage against Cassio and Desdemona.

Othello solicits Iago to kill Cassio and vows to kill Desdemona himself.

OTHELLO. Within these three days let me hear thee say
That Cassio's not alive.

I will withdraw,
To furnish me with some swift means of death
For the fair devil. [Desdemona].
(act 3, scene 3, lines 523–530)

Iago's attempt to kill Cassio with Roderigo's assistance fails, and Iago kills Roderigo to keep him from exposing Iago's plots against Cassio and Othello.

Othello kills Desdemona for what he believes is her infidelity with Cassio. Emilia discovers that Othello has killed Desdemona and reveals to Othello the extent of Iago's plot against him.

Iago kills Emilia for exposing his plot and then runs off, pursued by Montano and Gratiano, who soon return with Iago, followed by Cassio and Lodovico.

Othello expresses his anguish and his remorse for killing Desdemona and then kills himself.

OTHELLO. Then must you speak
Of one that loved not wisely but too well;
Of one not easily jealous, but, being wrought,
Perplex'd in the extreme; of one whose hand,
Like the base Indian, threw a pearl away
Richer than all his tribe;
... And say besides, that in Aleppo once,
Where a malignant and a turban'd Turk
Beat a Venetian and traduced the state,
I took by the throat the circumcised dog
And smote him, thus.

Stabs himself.
(act 5, scene 2, lines 392–405)

Lodovico is the last person to speak in the play. He blames Iago for the deaths of Othello, Desdemona, and Emilia and sends Iago to be tortured and likely executed for his villainy.

LODOVICO. (to Iago) O Spartan dog,
More fell than anguish, hunger, or the sea!
Look on the tragic loading of this bed;
This is thy work.
... (to Cassio) To you, Lord Governor,
Remains the censure of this hellish villain,
The time, the place, the torture. O, enforce it!
(act 5, scene 2, lines 412–420)

How does Iago use Cassio's punishment to exact revenge against Othello?

When Othello publicly scolds Cassio and strips of his rank, Iago is there to "pick up the pieces."  Cassio wants to regain favor with Othello, and Iago comes up with the plan to do it.  He tells Cassio to go to Desdemona and plead with her to speak on his behalf to Othello.  The irony is that Cassio is playing right into Iago's hands.  He has no idea that when Desdemona begs Othello for the reinstatement of his position, that Iago is going to use this to further advance his plan of revenge on Othello.  Iago questions Cassio's and Desdemona's relationship, planting a seed in Othello's mind that Cassio and Desdemon are in love and having an affair.  Iago's cunning use of Othello's jealous nature, is the impetus for his plan's success.

How does Iago demonstrate his skills as a villain in Othello?

Firstly, he admits it! In 4.1, he states "I am a very villain else."

Unlike villains who "know not what they do,"  Iago is in full awareness of the results of his actions.  He knows what he does is wrong, but he doesn't care -- he is after authority and power, and as we find out in the course of the play, the kingship itself, and he will stop at nothing to achieve his goal. What appears to motivate him is sheer hate.

One of his villainous techniques is compartmentalization -- telling one person or persons one thing, and another person or persons something else.  He can then play one off against the other, and by controlling the situation, implement his schemes.  In 2.3, he advises Cassio to ask Desdemona to have Othello reinstate him; Iago soliloquizes about how he will use that to manipulate everyone to his own purpose, "enmesh them all." He'll tell Othello that Cassio is seeking Desdemona so he can sleep with her, this will enrage Othello, discredit both Desdemona and Cassio, and put Iago in control.