One of the main themes of Othello is that of jealousy and what it can do to a person, and the eponymous main character Othello is Shakespeare's example of what can happen to a good but insecure man when he becomes jealous. One could easily argue that Othello is a more jealous character than Iago. He agrees too easily to go along with a plot to kill his wife and his lieutenant without any real proof that they are having an affair. He makes his decision based only on what Iago is merely suggesting to him without questioning Iago's motives. That being said, it is just as easy to argue that Iago is the more jealous of the two. He is terribly jealous of the fact that Othello promoted Cassio over him, and he is also jealous of Othello's popularity. Moreover, he suspects that Othello has had an affair with Emilia, his wife, saying " I do suspect the lusty Moor/ Hath leaped into my seat - the thought whereof/Doth like a poisonous mineral, gnaw my inwards (II,ii, 317-19).
Othello's jealousy caused him to kill his wife and himself. Iago's jealousy caused the deaths of Roderigo, his own wife Emilia, Desdemona, and Othello, and the wounding of Cassio. Whom would you say is the more jealous of the two?