2. Mark Zuckerberg
40u40 main mark zuckerberg
Age: 28

Founder and CEO, Facebook

Facebook's stock may have taken a beating since its $104 billion stock market IPO in May, but eight years after Zuckerberg founded the social network in his Harvard dorm room, it continues to dominate: 1 billion active users have uploaded a total of 219 billion photos and given a thumbs-up "like" 1.13 trillion times since launch. The company also released major updates to its mobile applications, and, reflecting Zuckerberg's philosophy of full steam ahead, the Facebook founder hired architect Frank Gehry to expand the company's already vast Palo Alto headquarters.

Mobilize: Zuckerberg is so attached to his smart phone, he used it to write his founder's letter for Facebook's S1 stock registration -- all 2,178 words of it.

--J.P. Mangalindan


  @FortuneMagazine - Last updated October 17 2012 05:11 PM ET
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