Managing director of renewable energy, GE Energy Financial ServicesRank: 36Why he matters: $4 billion. That's how much Walsh's division plans to spend on renewable-energy investments by 2010. In March he flew to Portugal to open one of the world's largest photovoltaic solar power plants. In May he announced that GE will invest $180 million in two giant Texas wind-farm projects. The company will also invest $50 million a year in promising startups -- making Walsh perhaps the leading sugar daddy of the green-tech boom.
Meet 50 Who Matter winner Gina Bianchini. Her site, Ning, lets anyone be a social networking mogul. (more) 
