Othello - Iago

"I will in Cassio's lodging lose this napkin,
And let him find it. Trifles light as air
Are to the jealous confirmations strong
As proofs of Holy Writ. This may do something.
The Moor already changes with my poison." - Iago (III.iii.322-326)

Iago is extremely cunning. I've been  blown away by how well he's manipulated people. He's made it look so easy. He convinced Roderigo not to commit suicide and to sell everything. He got Cassio drunk and got him fired, but then turned around and pretended to try to help him get his job back. At the end of Act III Scene iii, he actually becomes lieutenant. He convinced Othello, who was so sure of his love for Desdemona to want to kill her. Othello quickly jumped to the conclusion that his wife is cheating on him without confronting either one. Iago has everyone convinced that he's an honest, good person when he's really trying to get everyone killed.