1 of 19Michael Phelps, swimming (United States)
Phelps — the first U.S. male swimmer to compete in four Olympics — won't duplicate his eight gold medal-winning heroics from Beijing (he qualified in the same eight events, but will only swim seven), but history is still on the line. The 16-time medalist needs just three medals of any color to dethrone Russian gymnast Larisa Latynina as the most decorated Olympian of all time. And of course, the 14-time Olympic champ can extend his own record for the most gold medals. Just make sure you don't miss him chasing history: Phelps will retire after London.
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