I am going to say Donald Durry, a great fighter who unified the Welterweight title and then became Jr Middle champ, but it was effectively all over when he lost to average French pug Rene Jacquot at age 26! Some might say he's a two time champ and they would be right of course, but Curry was young and had it all before him before losing to Lloyd Honeyghan and then brutally KO'd by Mike McCallum. I just think that Donald Curry was a brilliant fighter who never fulfilled his true potential. He was retired by age 30, he should've been a fighter we all talk about as one of the top 10 fighters of the 80's. He blossomed for a short while without fully blooming.