In Shakespeare's Othello, Iago hates Othello and hopes to see him destroyed.
Iago believes that if he wants to get to Othello, the best way is to go through Cassio, who was promoted by Othello, over Iago. So Iago stirs things up so Cassio will find disfavor in Othello's eyes, hoping he can take both men "out." When Cassio laments what has happened, Iago assures Cassio that Desdemona can be of assistance in repairing his damaged reputation. In getting Desdemona to speak on Cassio's behalf, Iago is able to plant seeds of doubt, while leading Othello to suspect an affair between his wife and Cassio.
All the while, Iago plays one character off against another in order to find a way to pay back Othello. Iago hopes to have Roderigo (who once loved Desdemona) kill Cassio; Roderigo attempts this thinking he will then have a better chance getting Desdemona in the end. Roderigo attacks Cassio, who does not die, but then, under the pretense of rage at what Roderigo tried to do to Cassio, Iago kills Roderigo.
In terms of Iago's failure, Cassio does not die. However, Iago drives Othello into such a jealous frenzy, believing Desdemona unfaithful to him, that Othello kills his wife.
As news begins to come out regarding Iago's machinations, it becomes obvious that Desdemona was innocent; this is confirmed by Iago's wife, Emilia. Othello tries to kill Iago, but others there prevent him from doing so. Iago then kills his wife and attempts to run away (though he is caught). Othello is told he must stand trial for taking Desdemona's life, but being devastated by what he has done, he takes his own life.
At the end, orders are sent by Lodovico, for the execution of Iago. Iago is successful in destroying Othello, but Cassio is not killed as Iago had hoped, and in the end, Iago is himself put to death.