I'd have to say:

Larry Holmes- possibly the best HW ever
Sonny Liston- never was liked or accepted, iced Floyd Patterson twice, was older than he claimed and didn't get a shot at the title till late, underestimated Ali the first time and threw the second one for sure, ended being murdered by the mob or it would appear that way at least.
Dwight Muhammed Qwai/Braxton-hell of a short pressure fighter who beat many good fighters and gave Holyfield a tougher time than Mike Tyson did
Jose Luis Castillo-Despite recently screwin everyone with the weight nonsense, he is every bit as much of a warrior as MAB or Morales, and should have handed PBF his first loss but got screwed, gotta be one of the greatest lightweights of all time.
If I think of more I'll add em.