Roger Federer
It is widely debated that Roger Federer is the best tennis player of all time.
I think that tennis is one of those sports that you cannot truly enjoy watching unless you play. Otherwise, (1) you can't follow the scoring and (2) you can't have a true appreciation of how amazing the game play is. Like golf... it might look boring unless you can appreciate how extremely precise their shots are, and how difficult it is to do what they're doing.
Watching Roger might make you feel that it's not such a difficult thing, being a professional tennis player, because he makes it look so easy, so graceful. You can now watch his laser precision in slow motion.