I understand this is a hockey board, and that Gretzky is certainly deserving of the win, but keep in mind that Robinson was a tremendous athlete. In addition to being a world-class baseball player, he lettered in 4 sports at UCLA (Football, Track, Baseball, and Basketball). He won a National Title in the long jump, and was a running back for the Bruins in 1939 when an undefeated UCLA finished #7 in the AP Poll. Robinson also played professional football in Hawaii before World War II. Of course, Robinson is best remembered for breaking the color line and being a tremendous baseball player.
Gretzky is obviously the "Great One" for a reason, but when talking about "Greatest Athlete" I'll take Robinson.