Iago manipulates Cassio by instigating a fight between Roderigo and Cassio, hoping Desdemona will intervene on Cassio's behalf, making her husband, Othello, jealous and suspicious of their relationship. Manipulation is a repeating motif designed to influence characters through their weaknesses toward an ultimate goal.
In "Othello," Iago is a character who treats others as fools and manipulates them while devoting his life to revenge. Even his reputation as "honest Iago" is a manipulation. In this play, Iago is portrayed as the devil in action. His self-described "I am not what I am" is an anti-God, or devil, reference based on the Biblical passage Exodus 3:14 defining God as being "I am what I am."