No. 11

Paul Graham, 45
Co-founder, Y Combinator

No. of Angel Investments: 129
Companies funded (a sampling): Bump Technologies, FanChatter, Heyzap, Justin.tv, Scribd

The Harvard math PhD turned entrepreneur is one of the most active angel investors in Silicon Valley, through the innovative incubator he co-founded in 2005, Y Combinator. Twice a year, Y Combinator invites a group of fledgling entrepreneurs to come to Silicon Valley and participate in its three-month incubation program. Seasoned entrepreneurs help develop the ideas, and they also have weekly dinners where founders such as Facebook CEO Mark Zuckerberg drop by and give their advice. To date, Y Combinator has financed such startups as Scribd, Reddit, and Loopt with small stakes of $17,000 to $20,000. "Our goal is to make starting a startup one of the standard alternatives that ambitious people consider," Graham said in a telephone interview.