Should it have been called Othello or Iago?

Recently my College Literary studies class finished reading Othello by William Shakespeare. My professor gave us a day to mull over the whole story before we started a socratic seminar in further discussing the elements found in Othello. One of my classmates brough up an interesting question: Why is it called Othello and not Iago? Clearly Iago seems to steal the spotlight yet why does Shakespeare focus on the victims? The same question can be applied to his other stories such as Julius Caesar (Brutus), Romeo and Juliet (Tybalt and Mercutio).