In 2010, Tiger Woods' career earnings will reach the $1 billion mark, making him the first billionaire athlete. However, since Tiger Woods has such hefty taxes and management fees, he won't actually be a billionaire for another year or so.

According to Forbes, prize money from golfing only accounts for about one-tenth of his earnings. The rest comes from his prior and current endorsement deals from Nike, Tag Heuer, Gilette, Gatorade, Buick and Titleist.

Woods wouldn't be the first world-class athlete to become a billionaire. He would, however, be the first whose career has only involved playing a sport.