Who Are The Greatest Sporting Stars In The World?

Oh this is a really difficult question, how does one answering this kind of question without leaving someone out, this could be masters thesis, let alone a blurtit answer! I'll have a go at thinking of some people I can think of, but really you could answer this question for days:

1) Mohammed Ali (Boxing)
2) Jessie Owens (Track)
3) Pele (Soccer)
4) Ronaldo (Soccer)
5) Lance Armstrong (Six Tour de France wins)
6) Carl Lewis (Nine Olympic gold medals!)
7) Mark Spitz (swimming)
8) Jack Nicklaus (golf)
9) Pete Sampras, Bjorn Borg, John McEnroe (Tennis)
10) Michael Schumaker - Motor Racing (Formula One)
11)  Don Bradman (Cricket)
12) Steve Redgrave (Rowing)
13) Babe Ruth (Baseball)
14) Wayne Gretzsky (Ice Hockey)
15) Martina Navratlova (Tennis)
16) Eric Heiden (Speed Skating)
17) Jhangir Khan (Squash)
18) Michael Jordan (Basketball)
19) Roger Federer (Tennis)
20) Daley Thompson (Decathlete)
21) Walter Peyton (American Football)