Milo of Croton, the original Olympic star.
This article from the Times details the endorsement power that ex-Olympians have in marketing. Apparently it's a "for life" gig if you win once, or at least it can be.
I run a trivia contest on Monday nights, and when asked "who won the most gold medals in Olympic history?" no one, in all four rooms of the restaurant, knew the answer. (It was Raymond Ewry for track and field.) It's strange how in such a timeless event, even the most important stars are forgotten for the new faces. Star power is perfectly reflected by contracts; athletes who were once the face of Adidas or Nike are now pushing Cabot cheese.