Dustin Moskovitz

The world's youngest billionaire, Dustin Moskovitz was Mark Zuckerberg's Harvard roommate and Facebook's third employee. He is just 8 days younger than his friend. The two dropped out of Harvard and moved to California to work for the social-networking firm full-time; he was its first chief technology officer and then vice president of engineering. He left in 2008 to start Asana, a software company that allows individuals and small companies to better collaborate. Values of his new company: "pragmatism," "being a mensch," "admitting when you're wrong," and "chill-ness." Reportedly sold around a 1% stake in Facebook last year but held onto an estimated 5% in the company, whose value has soared to $50 billion, based on the recent Goldman Sachs transaction. Moskovitz signed onto the Giving Pledge in December; a photo of him and his live-in girlfriend Cari Tuna, a Wall Street Journal reporter who apparently will help him identify causes, accompanied his pledge letter.