He is frustrated about being overlooked for a promotion and sees an opportunity to retaliate against both Othello, who has wronged him, and Cassio, who represents that slight. Additionally, he suspects that Othello has been unfaithful with his wife, Emilia. He references this suspicion twice: "...
At the climax of the play, it is Iago’s wife, Emilia who exposes him. After Othello has strangled Desdemona and the Venetian councilors are trying to understand what has happened Emilia accuses Iago. He tells her to be quiet and go home but she becomes even more vociferous. Iago takes ...
EMILIA Alas, good gentleman! alas, good Cassio! IAGO This is the fruit of whoring. Prithee, Emilia, Go know of Cassio where he supp'd to-night. 130 To BIANCA. What, do you shake at that? BIANCA He supp'd at my house; but I therefore shake not. IAGO O, did he so? I charge...