Emil Zatopek, Marathon, Helsinki 1952
Credit: AFP / Getty Images

Imagine deciding to run a marathon on a whim – at the Olympics. That's what the legendary Czech runner did, showing up minutes before the race and then lapping the field, which included presumed favorite Jim Peters. Zatopek's surprising marathon win, combined with victories in the 5,000m and 10,000m, gave him a trifecta that will likely never be matched.