Iago gives several reasons for his hatred of Othello (usually to his confidant Roderigo). He says that he hates Othello because Othello passed him over for a promotion to lieutenant, choosing Michael Cassio (who he claims is much less qualified) instead of him. He also claims that he suspects that his own wife, Emilia, has cheated on him with Othello, making him a cuckold. However, it is unclear whether either of these are the real underlying reason for Iago's hatred—this is never completely clarified by Shakespeare.
