William Shakespeare, in writing the tragedy Othello, uses the jealousy motif that is apparent in many other types of literature written of a man and his downfall. Cain, in the bible, killed Abel due to jealousy. As did King Claudius in Hamlet, and the evil stepsisters in Cinderella.
"O, beware, my lord, of jealousy! It is the green-eyed monster." Just as Iago noted in Act three, scene three, lines one hundred and ninety-five to one hundred and ninety-six, jealousy would be Othello's demise. This jealousy, fed by the deception and dishonesty of Iago, manifested a new "view" of Othello's wife, Desdemona. Stricken with this disease, Othello goes as far as taking the life of his wife, along with his own. Although Othello's inability to fight off jealousy brought him down, his trustworthiness and frankness also led to his collapse. Othello never questioned Iago, and as honest as he may have appeared, anyone else would have needed more, not just one source for a charge such as the one Iago placed on Desdemona. Othello simply thought to highly of Iago, and never pondered whether he was truly honest.
Iago, with his keen ability to manipulate and create fallacies, placed jealousy upon the head of Othello. From there, it spread throughout Othello's body until it had embedded itself deep into his heart. Iago had won, and Othello was doomed from thereafter. Iago started this little devil, but Othello finished it off. Cassio's conversation with Desdemona at the opening of Act three played right into the hands of Iago. Here Iago brought suspicion into the picture, and said too much without saying enough. "I speak not yet of proof. Look to your wife; observe her well with Cassio; Wear your eyes thus, not jealous nor secure." Iago subtly plants suspicion in Othello's mind, and unaware as Othello may be, it is all that is needed to fuel his jealousy. Iago tries to run around the answer with Othello, giving clues that something is "in question," but doesn"t want to say it.