Serena Williams! http://www.huffingtonpost.com/2013/06/08/serena-williams-french-open-title-2013_n_3408191.html What a competitor! Singles tennis has got to be one of the hardest sports going...no "team" to back you up and playing against the world's best. The scores are close, so even the slightest slip-up can do you in. This takes a mental and physical discipline that few can hope to ever achieve. I remember watching Boris Becker win a 5 hour set in hot weather. At the time, I was 1/2 dead after one hour on the court with basic singles. While all the popular sports take conditioning and mental wiles, few leave you as alone to win or lose as tennis. It's a combination of all the best of the others....IMHO, anyway.