Tennis is a very difficult sport to earn money in. Only the very best players can earn a living out of it without sponsorship from elsewhere, and because it's an individual sport, there are only so many seats at the top table. Fortunately for Novak Djokovic, he's very good at tennis.
Playing in an era of tennis that's been dominated by Roger Federer and Rafael Nadal, Djokovic has emerged as the new poster boy of the sport. Still in his prime in his early 30s, he's won the prestigious Wimbledon tournament four times to go with two US Opens, one French Open and an amazing six Australian Opens. With a charming and charismatic personality, Djokovic's good nature and ability to communicate in several languages has seen him appointed as a UNICEF Goodwill Ambassador. He also sells a range of nutritional food products under the brand name Djokolife.