12. Paul Allen
Net worth: $17.5 billion
Paul Allen is the co-founder of Microsoft, the largest software manufacturer in the world. Allen went to the same high school as Bill Gates, the other co-founder of Microsoft. Before starting the company with his longtime friend in 1975, he dropped out of Washington State to work at Honeywell in Boston. He then left to start the company that propelled him into fortune. Allen left Microsoft after eight years when he was diagnosed with Hodgkin's disease, but he's been living happily ever since. Today, the 62-year-old Allen is the proud owner of both the Seattle Seahawks of the NFL and the Portland Trailblazers of the NBA. He is also a partial owner of the Seattle Sounders of the MLS. Forbes ranks Allen as the 51st richest person on the planet.