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.
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