Policarpo Díaz? very strong fighter, but he was not technically gifted and was unlucky enough to have to fight for the title with the freaking sweet pea whitaker. Wrong champion to challenge, bad luck, dude, maybe in another life. He was doing extremelly well in europe, and probably he could have been a world champion vs an easier champion. He was 32-0 with 23 yo when he faced pernell, but man, whitaker... too much for him. Too much for everybody, actually. Whitaker beat him up, and basically retired him with 23 yo. Had he fought another champion, he could have won, and grown, and be something special, who knows.
And he got 2 world title shots, 1 of which he didn't make weight for, the other he seems to have gotten an unluckly decision, both against black boxers when he was young and pre-prime