Michael Phelps has nothing to prove to anyone, but neither did Michael Jordan, Kelly Slater, or Gordie Howe. Still, these legends all got up off their laurels, un-retired, and tried to compete at a high level. Some succeeded. Others, not so much.
Why he hung it up: After finishing No. 1 on the Association of Surfing Professionals World Tour six times in the 1990s, Slater didn't have any real challengers.
Credit: Steve Robertson / ASP / Getty Images
Why he returned: Andy Irons. The late Hawaii native won three consecutive titles, motivating Slater to return to the sport full time in order to prove his supremacy.
His Success: Slater has had a helluva comeback career, with five ASP firsts since 2005.