Iago is considered as the most villainous antagonist in Shakespeare's novels. In Othello, his main motive for helping Cassio is to plan a revenge against him. He wanted to acquire the lieutenant position but it was awarded to Cassio. He thought that the Moor misjudge his capabilities and wanted to prove him wrong. And because of his jealousy of not receiving the appointment, he wanted to do something evil as far as being evil is concerned.
