Mark Zuckerberg

The creator of Facebook (FB) took Bill Gates' route: He dropped out of Harvard University and became a billionaire. In this photo, Mark Zuckerberg is projected wearing his trademark hoodie on an electronic screen in Times Square, New York, on May 18 during Facebook's initial public offering on the Nasdaq stock market. The social networking website went public four days after its co-founder and CEO turned 28. Fortune's 40 under 40 last year had Zuckerberg at No. 1.

Credit: Spencer Platt/Getty Images (image), Jason Henry McCormick/CBS (copy)