Iago is the antagonist of the play; in fact, his character is often cited as one of the clearest examples of an antagonist in all of literature. Iago actively works to thwart Othello by convincing Othello that Desdemona is being unfaithful to him, knowing that this belief will torment Othello. Part of what makes Iago such a chilling antagonist is his lack of clear motivation for tormenting Othello. Iago mentions that he believes Othello may have had an affair with Emilia, explaining “I do suspect the lusty Moor / Hath leaped into my seat” (2.1.). However, he doesn’t dwell on this possibility, and only mentions it infrequently, which suggests there are other reasons why he decides to destroy Othello. Iago also seems to be tormented by jealousy that others are rising to more prominent positions than he is; in the play’s first scene, we see him fuming that Cassio, who “never set a squadron in the field” (1.1.) has been promoted. Iago’s frustrated ambition might be an additional motivation for his behavior as antagonist, but his primary motivation seems to be a sadistic and megalomaniac desire to exert power over those around him.
Iago primarily acts independently, functioning as a master manipulator of those around him. For example, when Iago suggests the idea of Cassio and Desdemona’s relationship, Othello has to coax Iago into voicing his suspicions, but only because Iago has manipulated the situation so effectively. Because Iago is able to retain control of how other characters behave and how events unfold, he is seldom influenced by other characters. Iago is only significantly influenced by the behavior of another person at the end of the play, when his own wife turns against him and reveals him to be a villain responsible for all of the violence and suffering. Emilia’s betrayal makes Iago behave impulsively for the first time in the play: he stabs Emilia in front of witnesses. In the play’s ending, Iago shifts from a calculating figure always one step ahead of everyone else to a panicked killer trying desperately to save himself. In his final moments, however, Iago does regain some of his chilling composure: when Othello implores him to explain himself, Iago responds “What you know, you know / From this time forth, I never will speak a word” (5.2.). The rationale for his villainous antagonism is never fully revealed.