He was a top flight heavyweight with lots of talent. He had inadequate management and had some mental problems, (as in what was needed mentally to be optimally competitive.) His mental perspective was made worse by the burden thrust upon him by virtue of being a white heavyweight contender.
Heck the guy had to retire in his prime due to contracting HIV. He won one of version of the Heavyweight Championship and look at his record: 48-3-1 with 42 KOs.