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.

2. Jack Dorsey

40u40 jack dorsey square
  • Age: 36
  • Title: Co-Founder and CEO
  • Company: Square

It was Dorsey who shared the world's first tweet, "just setting up my twttr," and conceived the idea to share a brief "status." Now, as Twitter readies its monster IPO, Dorsey is the only cofounder of the initial trio (Biz Stone, Ev Williams, and him) who still works at the company. Dorsey had moved on to found Square, the vaunted mobile-payment system that now processes $15 billion annually (where he's CEO), but in 2011 he added the role of Twitter executive chairman and still helps drive big decisions. (See Jack Dorsey: The pride of St. Louis.)

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