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Sean Parker.
At the age of 19, he cofounded Napster, a file-sharing service that would change how the world consumes music.
By 24, he was the founding president of Facebook, a startup that was then tiny but would go on to become the biggest social network in the world.
The 35-year-old, whose net worth is now estimated to be about $3 billion, hasn't slowed down a bit. He recently launched Brigade, a social platform meant to encourage civic engagement, and donated $600 million toward his own foundation.
He's found a bit of controversy along the way, developing a reputation for being a big partier and an even bigger spender.