Sean Parker: $4 Billion
Sean Parker, 32, is perhaps best known for founding file-sharing music service Napster in 1999. In 2004, Parker, who served as an early adviser to social network Friendster, met with Zuckerberg after seeing "Thefacebook" on his roommate's girlfriend's computer. A few months later, Parker joined the social network as its founding president, signing Facebook's first investor.
Parker resigned as president in 2005 after police searched a vacation home he was renting and found cocaine. Parker was arrested on suspicion of possession, but not charged. He retained a 4 percent stake of Facebook, which could earn him $4 billion.