Iago gives several reasons for his hatred of Othello. He says that he hates Othello because Othello passed him over for a promotion to lieutenant, choosing 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, which is never completely clarified by Shakespeare.