Michael Jordan - a tad over-rated?! Lebron James?! My vote goes to Diego Maradona, Muhammad Ali or Tiger Woods.
I don't think athlete is the right word. Sports person would be more appropriate. IMO Woods might be the most famous.
If were being honest though, not many people do actually know his real name, being... =Eldrick Tont Woods.
Usain Bolt is massively popular and epitomises the word athlete. He's also Jamaican, which helps, because everyone likes Jamaica! And he's a super cool guy.