Not with you on Bird, I'd go with Jordan.
Boxer, not sure.
Soccer, Pele.
Bird could dominate any aspect of the game and he made every team he was ever on, great. Jordan was the third best player on his college team. He came into the league and they let him go wild and put up stats for ticket sales. But he has losing seasons all 3 years before Pippen (probably the real most athletic player in the league) came to town. What did Bird do in the meantime? Won a couple championships, beat Jordan 14 straight times (including 2 playoff sweeps). And Bird had to win against dynasty level teams like the Lakers, Sixers, Rockets, and Pistons. All's Jordan ever did was beat watered down teams led by the 80s A minus stars with David Stern's help.
You want to compare Bird and Jordan when they were at the end of their careers. Coming off two acl tears and a back condition that would have had every other player retiring, Bird led his team to 50 wins and he was still on verge to take out the Bulls if his back hadn't flared so bad that he was missing playoff games. Jordan in his last two years; two more losing seasons and no playoffs on 41 percent shooting. Bird never had one season like that. Jordan had freaking 5 of them. Sound great to you? He's a corporate illusion for obvious reasons; and like everything it comes down to money; not the truth.
As for boxing, I was considering Lennox Lewis and then I remembered Vlad Klit. LL actually beat VK; but that was b/c of a fluke cut that got worse throughout the fight. VK was actually ahead on the score card and in fact he's never finished a fight not ahead on the scorecard. Lewis didn't want any part of a rematch with that beast. He retired after that.