Gabe Newell is a rich man. Just how rich? According to a recent article in Forbes magazine, he owns over half the company he cofounded, Valve Software, which is estimated to be worth between $2 billion and $4 billion. That valuation pegs him as a member of the billionaires' club--or, conservatively, at least puts him close to it.

Valve cofounder Gabe Newell.

The key to Newell's success is Half-Life, Left 4 Dead, and Portal developer Valve, which has shown rapid growth in recent years. Last October, the company predicted 200 percent year-over-year growth, thanks in large part to its Steam online service. Speaking with the magazine, Newell said his company is, per employee, more profitable than Apple or Google.

According to Forbes, Steam controls half to 70 percent of the $4 billion market for downloadable PC games, thanks to the service's ease of use and mod-friendly features. It further explained Steam's success by outlining the company's profit sharing with publishers. At retail, publishers get 30 percent gross margin--on Steam, they get 70 percent.

Forbes' article also touched on Newell's battle with Fuchs' dystrophy, a congenital eye disease that eats away at the cornea. Newell eventually had cornea transplants in 2006 and 2007, which fixed his eyesight and gave him a new outlook on life--literally.

"The thing that snuck past my defenses was that not only could I see again but I could see better than I ever had before," he said. "I felt like I was in a fantasy story. It reminded me of how fast the future is coming at us and from what unexpected directions."