O, beware, my lord, of jealousy!
It is the green-eyed monster which doth mock
The meat it feeds on.
– William Shakespeare
Othello, Act 3, Scene 3. The devious Iago is being ironic when he warns Othello to beware of jealousy. In a powerful metaphor that has become part of modern English vernacular, he compares jealousy to a "green-eyed monster" that mocks the victims it devours. The cunning Iago is using reverse psychology here. His purpose is not to help guard Othello against the mental torture jealousy can bring about. It is to drive Othello to madness by inciting his jealousy over his wife Desdemona. This is foreshadowed in Iago’s speech.