The military hierarchy in William Shakespeare's "Othello" consists of Othello as the top-ranking officer, or general, Cassio as the second in rank, or lieutenant, and Iago as the third-ranking officer, the ancient. Aside from rank, each of these major characters also has a different heritage. Othello is a Moor, from northern Africa, Cassio is from Florence, a state independent of Italy at the time, and Iago is a Venetian.
Othello commands the armies of Venice, a status that's perhaps unusual because he's a Moor, not a Venetian. He has the confidence of the government's leaders, who trust his command in the wars going on with Turkey. He's respected by most but hated by Iago. Othello is married to Desdemona, a Senator's daughter, whom he loves to the point of extreme jealousy.
Cassio is promoted by Othello to the rank of lieutenant, and he's eager to please his superior. Despite his education, he's young and lacks military experience, and Iago feels he doesn't deserve the rank of lieutenant. When Cassio is then demoted by Othello, Iago advises him to use Desdemona to regain Othello's respect. Of course, Iago's motive is to make Othello jealous of Cassio.
Iago is the ancient, a military rank also referred to as the flag-bearer or ensign. He isn't happy with his position and is resentful of his superiors. Iago is disrespectful of Othello behind his back and plots to cause trouble between Othello and Cassio, making him the undisputed villain of the play.