From your reading of Act 1 scenes 1 to 3, analyse critically Iago's role in instigating Brabantio against Othello and Othello against Brabantio.
Iago is primarily driven by a desire for vengeance. He feels humiliated by Othello's choice to choose an outsider, the Florentine Cassio, as his lieutenant. Iago has applied for the position and feels that he is more qualified than the young and inexperienced Cassio for the post. He has rendered service to the general but he has, instead, decided to appoint a mathematician to be his second in command whilst Iago has to be satisfied with the lowly position of ancient. Even after three senators had appealed to Othello to appoint Iago, he ignored their recommendations and still chose Cassio.
Furthermore, Iago is clearly jealous of Othello since the general himself is an outsider who now occupies a rank far superior to his own. He is resentful of the fact that he has to bow to his authority. Added to this, Othello is a Moor, which Iago deems a revolting idea. This racist and prejudiced view is displayed in the terms he uses when referring to the general later in his discourse with Brabantio. To cap it all, Othello has eloped with the beautiful Desdemona, Brabantio's daughter, a woman Iago later mentions, he also desired.
In his conversation with Roderigo, Iago unambiguously states his intent when the aforementioned mentions that if he were in Iago's shoes, he would not still follow Othello:
O, sir, content you;
I follow him to serve my turn upon him:
In saying this he means that he would continue creating the perception that he was loyal to Othello whilst he was, indeed, plotting against him. He obviously wants to harm Othello in some or other way and we soon discover that he and Roderigo are out to blaspheme Othello's good name so that Brabantio, a senator, can take action against him. The purpose is to awaken Brabantio in the dead of night and inform him that Othello has kidnapped his daughter, Desdemona, and was abusing her. Iago hopes that the senator would become so upset that he would seek Othello's dismissal and arrest. The general would obviously be humiliated and Iago would have had his revenge.
Iago has acquired the help of Roderigo to whom he has pledged his assistance in acquiring Desdemona's affections. Roderigo is besotted with the beautiful young Venetian and would do anything to get her attention. He becomes putty in Iago's hands and does his every bidding.
When the two men arrive at Brabantio's home, they cry out to him awakening the angry senator whose rest has been disturbed. They inform him in the most graphic and foul terms of his daughter's supposed abduction by the general.
'Zounds, sir, you're robb'd; for shame, put on
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 clearly displays his racism here. He uses animal imagery to emphasize the so-called disgusting aspects of Othello's act. He demonizes the general by associating him with the devil and calling him 'an old black ram.' Iago and Roderigo are relentless and continue peppering Brabantio with the most repulsive and vile terms in order to provoke him into action.
'Zounds, sir, you are one of those that will not
serve God, if the devil bid you. Because we come to
do you service and you think we are ruffians, you'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.
Their strategy works and Brabantio is livid and completely overwrought by the idea of his daughter's supposed abduction and abuse. He is driven into action and raises the alarm, arousing his entire household.
Strike on the tinder, ho!
Give me a taper! call up all my people!
This accident is not unlike my dream:
Belief of it oppresses me already.
Light, I say! light!
Once Iago is convinced of their success, he takes his leave, telling Roderigo that he has to join Othello to create the impression that he is supporting the general against Brabantio's malice. He leaves Roderigo to further deal with Brabantio and then slips away to Othello. Brabantio is stricken and tells Roderigo that he wished that he, Roderigo, had had Desdemona, considering the circumstances, for he had previously forbidden the young lovesick Venetian access to his house or his daughter.
Iago's scheme, however, fails miserably in the end for Othello is neither sanctioned nor dismissed and is rather sent on a mission to defend Cyprus against a possible invasion by the Turks. This happens after Desdemona comes to her new husband's defense. Brabantio ends up a bitter man who feels betrayed by his daughter.