Perhaps the most obvious subject or theme in Othello is revenge and jealousy . Iago is the key to almost everything that happens. He has been passed over for promotion, so he dislikes Othello and must be jealous of Cassio. He thinks Othello might also have slept with his wife. However, we can never be completely sure what motivates Iago to be so destructive - he manages to get Cassio dismissed but then Iago doesn't seem interested in Cassio's job, only in causing more problems. We also learn that Iago has tried many times in the past to steal the handkerchief that means so much to Othello. This tells us that he was planning against Othello long before his promotion was blocked.