Why do I say this? Fitzsimmons was the first man in history to be a triple crown champion: Heavyweight title (Ko in 14th over Corbett), Light heavyweight and Middleweight. Fitzsimmons only weighed in at 167lbs while he fought much bigger men; one in particular I read was 6'7" and over 240lbs. He was in an era when referees were not so wimped up when they saw blood; since Fitzsimmons killed two men in the ring, as far as my knowledge. He fought the best competition in the world for over 31 years as a professional and learned from the best. He had numerous exhibitions, was fast as can be; his exhibition with a man in a padded suit shown he could land well over 100 punches in three minutes to his opponents six.
Sure Robinson was great, he fought alot of top guys and held the middleweight title five times, but he was better at welterweight. Sure Greb amassed such a convincing fight record, but 117 of those fights were no decisions.
Fitzsimmons is among the greatest fighters of all time...and he should be up there with Robinson and Greb as the greatest pound per pound.
Fitzsimmons: The Greatest Pound Per Pound
Fits never did anything with the titles he won though. He was not a great champion at any of those weights which hurts his standing. I agree him winning those titles is impressive and makes him a great, but if he only held on at least one of those titles for a string a defenses. He never dominated a weight class like RObinson did.