Clay's achievements weren't in the Olympics though. They came later as a professional.
Can't disagree on Jesse Owens at all - he was remarkable. But for me his achievements had more of a political/ social impact than anything else. It may not have been his fault regarding the defending of his titles but he didn't.
If the Olympic ideal is all about pushing the boundaries of what humans are capable of and proving you're the best in the world over decades then it's Phelps and it's not even close.
Correct. It depends on which criteria you use, so everyone will have a different opinion.