O, beware my lord, of jealousy!
It is the green-ey'd monster which doth mock.
The meat it feeds on. That cuckold lives in bliss
Who, certain of his fate, loves not his wronger;
But, O, what damned minutes tells he oer
Who dotes, yet doubts, suspects, yet soundly loves!
This is what Iago tells Othello, as if he is a concerned friend, warning Othello that his wife has betrayed him. He continues to tell Othello of how he suspects Desdemona (Othellos wife) of adultery with Cassio, Othellos lieutenant. He does this so that Iago himself can up his military prestige by taking on Cassios role as lieutenant. He whispers deceit in Othellos ear, until Othello becomes so convinced of Desdemonas guilt, that he kills her. This characterization of Iago and Othello promote, amongst others, the themes of jealousy and deception, in William Shakespeares' tragic play Othello.
Iago is characterized as one of Shakespeares' most treacherous villains. He is very quick with his tongue, and so easily convinces many of the other characters to do his bidding, of which Roderigo is a perfect example. When Cassio was promoted as Othellos lieutenant, Iago immediately became jealous of him. In Iagos view, Iago himself should have received that promotion; after all, Cassio had no battle experience as Iago did, although he had studied for it. It is this jealousy that brings out Iagos treachery, and makes him determined to do anything in order to gain a higher military position. He tells us;
Others there are
Who trimmed in forms and visages of duty
Keep yet their hearts attending on themselves
And throwing but shows of service on their lords
Do well thrive by them, and when they have lined their coats