“Greatest” SWIMMER- Yes. Athlete, NO. Decathlon winners are the best ATHLETES. Bob Mathias won 2 at age 17 and 21
I'll add in Rafer Johnson...for winning the decathalon in 1960, getting to the top of the steep stairs in 1984 to light the cauldron at age 49, and for looking real good today at the age of 76 :o)