Why does Iago choose Michael Cassio as an instrument of revenge against Othello?
By provoking Othello's jealousy toward Cassio, Iago effectively kills two birds with one stone, inflicting harm on both his superior and the man whom his superior has chosen to take a position that Iago believes to be rightfully his. There are three other aspects of Cassio's character that make him a prime candidate for Iago's scheme. First, Cassio is known to have a problem handling his cups: if he can persuade or trick the lieutenant into drinking, it is likely that an inebriated Cassio will commit some form of misconduct. Second, Cassio is inordinately concerned with his reputation. If his good name is blotted, Cassio will seek to rectify the stain through an appeal to Othello. Third, Cassio is a lady's man. Not only does he have Desdemona's ear, he is known to have sexual affairs with women of questionable backgrounds, notably the courtesan Bianca, whose jealousy reinforces Iago's cause of casting doubt upon Cassio's fidelity.