I agree that the Decathlon is the ultimate test of an all-rounder.
However there were two athletes (Bob Mathias and Daley Thompson) who also won two Olympic Gold medals in the Decathlon.
How do you compare them to Eaton?
My vote for your (rather vague) title goes to Jesse Owens:
he set three world records and tied another, all in less than an hour at the 1935 Big Ten track meet in Ann Arbor, Michigan—a feat that has never been equalled and has been called “the greatest 45 minutes ever in sport”
he went on to win 4 gold medals at the 1936 Summer Olympics in Berlin, Germany ( 100 meters, 200 meters, long jump, and 4 × 100 meter relay.)
If the answer to this question can be immediately followed by who?, then it’s prob not the right answer - re Ashton Eaton. TWO gold medals in the decathlon is really significant, though, agreed. The injury toll the decathlon puts on an athlete’s body is brutal, so to peak twice and beat the best of the world on the biggest stage really does take outlandish ability.
Canadian Bill Werbeniuk was an international dual sport athlete - world level snooker and pool player, albeit a level below the very best, but an elite, world champion bevvy merchant. Could drink 40-50 pints of lager a day.
Three men have won 2 Decathlon Olympic golds so i would go for someone else. For me it’s Michael Johnson. It wasn’t just the amount he won, it was his domination of the races.
You also need to bring Jim Brown into the discussion. Not only is he in both the NFL and Lacrosse Halls of Fame, but in college he was also an excellent basketball player, and was on the track team.
For a single sport, In terms of being so far above his peers then Don Bradman has to be in contention. What he did is 50% better than anyone else has ever done. A statistical freak
Add me to the Thorpe list. Keep in mind that, when the Olympics had both a track & field (athletics, for those of you outside of North America) pentathlon for men as well as the decathlon, he won both in the same Olympics.
I have a feeling the best athlete “ever” is somebody whose name, and possibly feats as well, has been lost to time for centuries.