Final answer:
The quote "O beware, my lord, of jealousy: It is the green-eyed monster, which doth mock // The meat it feeds on" is found in Shakespeare's play Othello. Iago warns Othello about the destructive nature of jealousy using this metaphor.
Step-by-step explanation:
The quote "O beware, my lord, of jealousy: It is the green-eyed monster, which doth mock // The meat it feeds on" is found in Shakespeare's play Othello. In Act 3, Scene 3, Iago warns Othello about the destructive nature of jealousy using this metaphor. Iago uses the color green to represent jealousy and describes it as a monster that feeds on its own essence and destroys everything around it.