Have to agree with Robinson, Armstrong, Wilde, Pep, Leonard and Ali, but what about Archie Moore? He fought a long time and was well into his 40's (or even older) when he finally retired. I believe he holds the record for the most KO's. Took him a long time to get a shot at the light heavyweight title, most guys were probably afraid of him. Downside, didn't have any success at heavyweight.