Othello's villain, Iago, may be literature's most impressive master of deception. Iago plots with consummate sophistication, carefully manipulating Othello (without any real proof) into believing that Desdemona has been unfaithful. His understanding of the human psyche is phenomenal, as is his ability to orchestrate a complicated interweaving of pre-planned scenarios. Iago's deception is potent because of his patience, his cleverness, and what seems to be his intrinsic love of elegant manipulation.
In Othello, Iago orchestrates Othello's downfall like a skillful playwright.
Iago's ultimate deception is not of Othello, Cassio, or Roderigo: it is of the audience. By refusing to tell Othello his motivations in Act 5, he is also refusing to tell us. We are strung along through Othello in the belief that all will be revealed, but it seems that the joke is on us.