For example, when the two are discussing Desdemona, Iago says: O, beware, my lord of jealousy!

It is the green-eyed monster, which doth mock

The meat it feeds on. That cuckold lives in bliss

Who certain of his fate loves the wronger,

But, O, what damned minutes tells he o'ver,

Who dotes yet doubts, suspects, yet fondly loves. (III.iii.166-71)

Here we see an example of Iago's cleverness. He warns Othello about jealousy, appearing to be concerned, knowing that Othello will not be able to contain his emotion. Once the thought of infidelity has entered his mind, it can never be erased. With very little effort, Iago has set Othello up for a great fall. Iago also displays how clever he is with the handkerchief. Iago is a dangerous villain because he is intelligent. He thinks things out and carefully plots his moves. He knows how people operate so he can use their weaknesses against him.

Another characteristic that allows Iago to manipulate Othello is his own jealousy. Iago is not reasonable in his feelings regarding being passed over for lieutenant. Instead of talking to Othello, he becomes enraged at those who would rather honor their masters and he allows his jealousy to rule...

He is much like Othello in that once an idea is planted in his mind, he does not forget it easily. Iago chooses to act out instead of behave rationally. He decides that the one thing that would make him feel better is revenge. His jealousy has positioned him to hurt many innocent people in play, with the most innocent being Desdemona. His ability to hurt her and use Emilia without any emotion demonstrates the power of jealousy, not to mention the depth of what Iago will do to make himself feel better. He is behaving like a child and does not care to behave any differently.
Iago is one of literature's greatest characters because he is evil through and through. Never once do we see a gentle caring side of this man and never do we feel any bit of remorse for him. He is evil and he is proud of it. He is not motivated by goodness and certainly not impressed by it. He is also very smart, which proves to be dangerous for a man with only evil intentions. He is good at gauging people and not outsmarted by anyone in the play. He understands how people operate and uses this to his advantage. His own jealousy motivates him and allows him to be the perfect bad guy.

Work Cited

Shakespeare, William. Othello. New York: Penguin Books. 1968.