Mark Zuckerberg is a brilliantly intelligent Harvard student, who is unapologetically arrogant due to this. He is shown to be ruthless and driven by the knowledge that he is bound to be successful. In the quest to make Facebook popular, he begins to make poor choices resulting in the loss of close relationships and friendships, which Zuckerberg later comes to regret.
Personality… selfish, caustic, and defensive. Mark is never without a quick, biting comeback on the tip of his tongue, just waiting for a perceived slight to present itself. Mark cannot stand to be thought of as dumb or lesser by anyone, and tolerates geniuses and fools with almost equal measures of scorn. His ability to form personal relationships is further hindered by the fact that he is mercilessly logical, willing to cut out anyone that might threaten his success. Still, he’s not totally devoid of conscience, and in private moments seems uncertain about the path his life has taken.
Eduardo Saverin is a fellow Harvard student and initially one of Zuckerberg’s closest friends. He is the first to put faith into the idea of developing Facebook and invests $1,000 in helping Zuckerberg develop the website. However, he soon finds himself being used and betrayed by Zuckerberg and Parker, who eventually manage to dilute his shares in the company.
Sean Parker is a brilliant but no longer successful young man, who founded the music sharing site Napster. He is a party boy and drug abuser but also very quick to pick up on the potential that Facebook could have, and as such capitalizes on this by becoming good friends with Zuckerberg. His manipulation eventually comes to an end, when Zuckerberg recognizes him for what he really is.