There are many great boxers who achieved glory at lower weight classes and moved up to heavyweight. But only a handful of them could actually taste success at the highest (heaviest) level. So, who is the greatest heavyweight with great success at lower weight classes? Is it Bob Fitzsimmons? Gene Tunney? Ezzard Charles? Michael Spinks? Archie Moore? James Toney? Oleksandr Usyk? Or somebody else?
Ezzard Charles hands down. Best lighheavy ever and was a beast at 160. Not going to be popular on classic, but Uysk is another guy that is just special. He is not a natural heavyweight in this era but it simply doesn't matter because he is that good. Michael Spinks is right up there as well. James Toney gets an honorable mention as well.
My own vote goes to Evander 'the real deal' Holyfield. Great success at cruiserweight followed by an ATG resume at heavyweight.
Holyfield is my highest ranked HW who either won a title or had notable success below HW. Of my top 20 HWs of all time, Langford ranks the highest p4p and had significant success below HW.
Much as I love Usyk this would probably be my answer by a hair. Holy is worth consideration, but I can't rate him because he was getting HGH delivered to his house under the name "Evan Fields."
Tunney and Langford are the best HWs to win belts at LHW and MW. When looking at the HW GOAT conversation they are really the only 2 participants who have feats in the lower weight classes. In terms of way lower weight classes its Stribling or Mickey Walker. Stribling started at FW and won the WBA HW title in December 1930. Mickey Walker was a WW champ who drawed with Jack Sharkey.