40 under 40

Our 2013 edition of the list features young hotshots who are rocking businesses as diverse as air travel, natural gas, and genetic coding, as well as—if you can believe it— government.

24. David Karp

40u40 david karp tumblr
  • Age: 27
  • Title: Founder and CEO
  • Company: Tumblr

When Karp dropped out of high school at age 15, it wasn't without a life plan: "I wanted to drive software, and I wanted to build stuff on the Internet," he recalls. The rest is history: He built Tumblr, which hosts over 136 million blogs, and sold it to Yahoo earlier this year for $1.1 billion. Under its new parent—and CEO Marissa Mayer (see No. 1)—Tumblr is reportedly aiming for $100 million in sales this year from advertising, up from an estimated $13 million generated last year.

  @FortuneMagazine - Last updated September 30 2013 03:41 PM ET
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