Biff Loman is Willy's son and it is the conflict between the two that the story of the play revolves around. Biff was a star football player in high school, with scholarships to two major universities. He flunked math his senior year and was not allowed to graduate. He was going to make the credit up during the summer but caught Willy being unfaithful to Linda. This shock changed Biff's view of his father and everything that Biff believed in. Biff then became a drifter and was lost for fifteen years. He was even jail for stealing a suit once. But now, he has come home and the problems begin.
Willy wants dearly for Biff to become a business success, although Biff has an internal struggle between pleasing his father and doing what he feels is right. Biff wants to be outside on a cattle ranch, and Willy wants him behind a corporate desk. Through the illusions that Willy believes, he cannot see that Biff is a nobody and not bound to be successful as defined by Willy. This conflict is the main material of the play.
Eventually, Biff finally sees the truth and realizes that he is a "dime a dozen" and "no great leader of men." He tells this to Willy who is outraged. Willy shouts, "I am not a dime a dozen! I am Willy Loman and you are Biff Loman!"
At the end of the play, Biff realizes the illusions that Willy lived on. Biff is destined to no greatness, but he no longer has to struggle to understand what he wants to do with his life.