4. Sergey Brin & Jack Dorsey (Tie)
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Dorsey (left) and Brin (right)

Sergey Brin
Age: 39
Co-founder, Google

Brin might have the best job at Google: turning science fiction into reality. The search giant's co-founder stepped down as president of technology in 2011 to focus on the fun stuff dreamed up in the super-secretive Google X labs. Take "Project Glass," which he unveiled in June. The goofy-looking computerized glasses let users watch videos and browse the web via a tiny display in their line of vision. In his spare time, Brin (along with his wife, 23andme CEO Anne Wojcicki) has become a bigtime philanthropist, donating $132 million to the battle against Parkinson's disease.

Cash pile: Brin's net worth is estimated at $20.3 billion. —M.L.

Jack Dorsey
Age: 35
Founder and CEO, Square

Co-founder and executive chairman, Twitter

The consummate multitasker no longer has a day-to-day role at Twitter but he's been on a tear at Square. The fast-growing payments company has signed on more than 2 million customers, including both Romney and Obama campaigns, which use it to collect donations. In August, Square signed its biggest merchant yet: Starbucks, the king of lattes. Dorsey personally flew to Seattle to seal the deal with Starbucks CEO Howard Schultz, who now sits on Square's board. As part of the agreement, Starbucks invested $25 million in Square, helping to raise the startup's estimated valuation to a whopping $3.25 billion. Not bad for a deal that was sealed in the virtual blink of an eye.

His dream job: Mayor of New York City.

--M. L.

  @FortuneMagazine - Last updated October 17 2012 05:11 PM ET
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Organizations headed by some of these top young minds in business have grown this past year, many of them hiring at an impressive rate. Here are seven examples.

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