Dan O'Brien and Dave Johnson
Decathletes aren't typically endorsement centerpieces, but after America's Dan O'Brien set a world record for points in the event in the run-up to the 1992 Olympics, Reebok ran a campaign that built up the rivalry between him and fellow American Dave Johnson. This ad touts a battle in Barcelona "for the title of World's Greatest Athlete."
The hype backfired when O'Brien failed to qualify for the Games. Johnson suffered a stress fracture, but still managed a bronze. O'Brien did take the gold in Atlanta four years later.