Age: 25
Occupation: Tumblr founder and CEO
The tech world is full of college dropouts, but serial risk taker Karp ended his formal education at 15 and took a job as CTO of Urban Baby before he was even allowed to vote. At 20, frustrated with the options of other blogging platforms and eager to explore the burgeoning world of social media, Karp created the trendy blogging platform Tumblr and never looked back. Forty-nine million blogs, 19 billion posts and one dropped e later, Karp's site has successfully synthesized blogging and social, and given tens of million of users an outlet for their own creativity.