11. Sergey Brin
Sergey Brin
Co-founder, Google
Age: 38
Industry: Technology

After sharing responsibility for Google's day-to-day operations for 10 years, Brin and Larry Page are officially decoupled -- on this list and at the Googleplex. With Page running the show, Google's other golden boy now devotes his time to special projects, many of them in stealth mode.

Cutting loose: Billionaire Brin is apparently having some fun too. His Google page shows newly uploaded photos of himself skydiving and scuba diving in Egypt's Red Sea. He has also invested $5 million in a Virginia-based space tourism company and is waiting for his private ride into space.

Last updated October 25 2011: 5:11 PM ET
Join the Conversation
Ones to watch

In addition to Fortune's 40 Under 40 list, we're also keeping our eye on these 20 innovators, young guns from a wide range of industries and backgrounds.