27-year-old Dustin Moskovitz, co-founder of Facebook, is the world’s youngest billionaire. Net worth: $3.5 billion.
Mark Zuckerberg, chief executive officer of Facebook, is 8 days older than his former roommate Dustin Moskovitz. Net worth: $17.5 billion.
At 19, Sean Parker co-founded Napster. Now he’s diving back into digital music with an investment in Spotify, the popular music subscription service. Age: 31. Net worth: $2.1 billion.
John Arnold runs Houston hedge fund Centaurus Advisors, a specialist in natural gas trading. Age: 37. Net worth: $3.5 billion.
Along with his brother Frank, Lorenzo Fertitta bought mixed martial arts outfit Ultimate Fighting Championship for only $2 million in 2001. The league now propels him into the Forbes 400. Age: 42. Net worth: $1.2 billion.
Ken Griffin, the founder and CEO of Citadel Investment Group, began investing as a Harvard undergrad after he read a Forbes article about the Home Shopping Network. Age: 42. Net worth: $2.3 billion.
French-born Iranian Pierre Omidyar moved to the U.S. with his family at age six. He became a billionaire in 1998 when his company EBay went public. Age: 44. Net worth: $6.2 billion.
Newcomer Mark Pincus, founded social media gaming company Zynga in 2007. The company has piggy-backed on Facebook’s success. Age: 45. Net worth: $2 billion.