Iago motivation was to become a lieutenant but Othello didn’t promote him to that rank. Since then Iago started to hate him and go behind his back and do bad thing and Iago calls him the Moor. He also want to destroy Othello’s new marriage, by making him believe that she is having a affair with Cassio.  Even on his marriage day Iago went to tell Brabantio that his daughter is marrying Othello. As think he is a pretty good being a snitch and trying to get after Othello just because of him not getting what he thought he deserved.