Like most sports, boxing loves lists. And lists about the heavyweights—especially the eternal question of who was the all-time best—have been around as long as the title itself. Most serious historians today agree on the top two slots: Muhammad Ali and Joe Louis (or Joe Louis and Muhammad Ali). But from Number 3 on, it's pretty much wide open. Monte Cox is a terrific boxing historian whose research I have drawn upon and learned from. His heavyweight ranking is as solid as anybody's, and he even explains his choices. And for what it's worth, his Number Three is my Number Three!