If your question is about the best natural all around athlete in history it is Jim Thorpe.
He was a top professional at several sports, won the decathlon and pentathlon at the same Olympics.
Many are better at one sport but he was great at almost anything he did.
According to the modern day world of athletes it is Michael Phelps. No doubt an exceptional athlete who is very fit.
But I have to say Bruce Lee. For being such a small guy he was doing incredible feats of strength, power, cardio, and stamina. His fitness was off the charts.
Jesse Owens or Jim Thorpe or Carl Lewis
Pele
