History's Most Impressive Weight-Jumper?

Which means he started off as a lightheavy and then ate himself to heavy very quickly.

 

By choice. He fought at middle in the Olympics and chose to fight as a professional heavyweight.

There was nothing natural (except his body, I presume) about Chris Byrd as a heavyweight...and yet he won two titles and fought a who's who in the division...Ibeabuchi, Vitali Klitschko, Wladimir Klitschko, Holyfield, Tua, Holyfield, Oquendo, Golota, McCline, Williamson, Povetkin...that's about as good as you'll find as far as a championship level fighter's list of opponents...and you likely could've added Lewis to the list if Lennox had wanted to make the fight at the time.

It wasn't a one-fight stay, but it was still a weight jump...he put on roughly 40 pounds in his first year or two as a pro...and then fought virtually the remainder of his career at that inflated weight.

 

As I said, a guy who was 5'6 and fought at 135lbs(which is not shocking for a man of that size) early in his career was withheld from that achievement only because of shameful ducking and would absolutely flatten a guy like Ruiz.

 

But then, factor in where John Ruiz started his career.