Bob Fitzsimmons, Sam Langford, Harry Greb, Henry Armstrong, Sugar Ray Robinson, Ezzard Charles. One of them is.
Hopkins entered his prime 4 years later. Toney was weight-drained. Hill came of a loss to DM. McCallum was past prime and far above his best weight. And compare that to Henry Armstrong: He had 61 fights from 1937 to 1940. Of those 61 fights he won 59, 51 by knockout. In this time he became the featherweight world champ, the welterweight world champ and the lightweight world champ. He held those titles at the same time. He also set the record for welterweight title defences. A record that still stands today. In this time frame he fought 10 Hall of Fame fighters 13 times. He fought ranked contenders more ofthen than Roy Jones Jr. had fights. That´s a no comparison.
There isn't one definative NO1 ATG imo. Greb, Armstrong, SRR, Langford (My choices) all have a good claim and can be argued into the NO1 spot.
I think Sugar Ray Robinson was all those things in one. At one time in his career, I think his record was 128-1-2. How impressive is that!
I'd say Robinson, great speed, one punch KO power, amazing technical skills and he beat more hall of fame fighters than anyone in history. Yeah it was but La Motta weighed 19 lbs more than him in that fight. That would almost be the equivalent of Floyd fighting in the Super 6 (give or take 2lbs - you get the point). Plus Ray beat him 3 weeks later (with a tune up fight in between) and then finished their series 5-1.