Fountain of Youth: The Under 30 Hall of Fame

Photograph Courtesy Facebook
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Mark Zuckerberg, Facebook

A member of our inaugural 30 Under 30 list, this Zuckerberg launched the wildly popular social networking site in February 2004 with the help of some Harvard buddies. More than two-thirds of the school's students signed up in the first two weeks, and four years later, the site has more than 100 million users.