Founding partner, Y CombinatorRank: 46Why he matters: It takes a true nerd to make a science of venture capital investing, but Graham specializes in turning complex theories into marketable businesses. In the 1990s he launched Viaweb, one of the first companies to help ordinary people build online stores. He also pioneered the use of esoteric Bayesian statistics to filter junk e-mail, effectively making him the father of today's antispam tools.
Y Combinator, his new seed fund, takes a hands-on approach to nurturing startups by combining active mentor-ship with relatively modest dollops of cash. He may be onto something: Web 2.0 services Loopt, Reddit, and Justin.tv have prospered with funding from Y Combinator.
Meet 50 Who Matter winner Gina Bianchini. Her site, Ning, lets anyone be a social networking mogul. (more) 
