For me it's Larry Holmes. I never gave him the recognition he deserved when he was Heavyweight champ. Now I watch his fights all the time and he is one of the best boxers the heavyweight division has ever seen
Lennox Lewis. I viewed him as a guy who just beat up on past prime heavyweights. I felt he either was lucky to not face them in their primes or outright avoided them. After Lennox retired and I went back and watched his fights, he truly was a great fighter IMO. He would be a tough out for any heavyweight who ever lived.
In the early years I was much the same. But by the time he was basically the last man standing I realised how good he actually was. As time has gone past I've come to respect him more and more.
Pernell Whitaker. Hated all Duva fighters back then, except for Rocky Lockridge. Especially how puckish Whitaker could be, how he'd refer to himself at times in the third person, all of it. Plus he beat Haugen and Nelson while losing perhaps one of the 24 rounds in the two fights. Later on, distance being the great tranquilizer, I began to appreciate how massively great he was, and he also humbled Don King's concubine Chavez. That was both immensely satisfying and infuriating at the same time.
James Toney for me. I started watching boxing around the time he was floundering around, losing to Drake Thadzi. When he beat Jirov and Holyfield, I didn't appreciate what I was witnessing
Mike Tyson. The thing he was convicted for really bothered me, and I cheered when Holyfield and Lewis knocked the crap out of him. Being on here and reliving his past fights have me a fresh admiration of him. Even the lame Jones and Paul fights haven't diminished my admiration.
I was late to the party to appreciate Joe Calzaghe. The evidence eventually caught up with his fan base.
Carl Froch for me. I thought He was slow and robotic (Which He kinda was). I thought He had no defence (Wasn't his strongest side obviously) I thought He was lucky to get some decisions, namely against Dirrell and Glen Johnson (I still do believe that) I found him annoying due to his arrogance (I still do. I think He has a pretty popular Youtube channel. I sometimes get it recommended to me, but never clicked on anything). ...but saying that, He still had a really good, eventful and enjoyable career - He was a true warrior who fought everyone in his era, gave us some truly outstanding fights and achieved much more than probably anyone expected. Anyone other than "The Cobra" himself, obviously ).