In Shakespeare's, Othello, perhaps Iago is the worst of the Bard's villains. Iago is jealous because he was passed over for a promotion; when Cassio is promoted instead, Iago plans to destroy the man. And to do so, he strikes where Othello is most vulneralbe—his heart. For not only is Othello newly married and in love, but he is ferociously jealous and, with help, loses his faith in Desdemona.
To destroy Desdemona and Cassio (who are really only casual acquaintances), Iago plants false evidence and spreads untruths so it seems as if Desdemona and Cassio have been sleeping together.
To get Roderigo to attack Cassio, Iago lies and says that Desdemona is tired of Othello and is having an affair with Cassio—their lips are so close, Iago says, they might as well be kissing.
Lechery, by this hand; an index and obscure prologue
to the history of lust and foul thoughts. They met so near
with their lips that their breaths embraced together.
Villainous thoughts, Roderigo! (II.i.268-271)
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