In Act I of Othello, Iago says to Roderigo:
I am not what I am. (I.i.57–65)
The line is verbal irony (understatement) because, even after Iago admits this secret, Rogerigo continues to trust him and pay him money, knowing full well that he is a liar, cheat, and traitor! This is why Iago calls Roderigo his "fool."
This reveals Iago's status as a Janus figure. Janus was usually depicted with two heads facing in opposite directions. Janus was two-faced, a perfect analogy to describe Iago. Iago seems to be honest and loyal to Othello, but in reality, he is a vice character and a satanic villain. This line reveals one of the main themes and motifs in the play: appearance vs. reality.
The line is a spoof of one of the great verses of the Old Testament. Yahweh (God) says, "I am that I am." He means He is what he says he is, and He will do what he says He will do. Here, Iago reveals just the opposite: he is not who he says he is, and he will not do what he says He will do. Iago and others say he's "honest." He says to Othello, "I am your own." And he says he will kill Cassio. He is none of these. He will not do any of these. Iago is a two-faced liar.
In the Othello's opening scene, Shakespeare reveals to his audience almost immediately what Iago's true character is. After Iago discusses with Roderigo his being passed over the Othello's lieutenant position, he establishes not only what his plan is to get what he wants but also tells the audience who he really is. Iago's speech reveals that he is:
1. Twofaced--in the several lines, Iago gives many examples of people who pretend to be lowly and humble in order to get better positions, wealth, or recognition and admits that he is such a person.
2. Astute--when it comes to human nature, Iago's words demonstrate that he has studied how humans work--how they are susceptible to flattery, what really motivates them, and how to cause their downfall. Iago announces at the end of his speech,
"I will wear my heart upon my sleeve / For [birds] to peck at: I am not what I am" (1.1.67-68).
His words not only illustrate his two-faced nature but also show that he knows enough about others' personalities and trust that he will be able to fool them into thinking that he is someone completely different than who is really is.