Michael Jordan
Credit: Andrew D.Bernstein / NBAE / Getty Images

Why he hung it up: The first time Jordan retired he wanted to play baseball, had won everything he wanted to, and was likely gambling too much to dedicate himself to the game.

Why he returned: Because he's quite possibly the most competitive person on the planet.

His success: Jordan led the Bulls to three-straight championships between 1995 and 1998. He had decent personal stats with the Washington Wizards between 2001 and 2003, although the team didn't perform and he singlehandedly ruined No. 1 pick Kwame Brown.