2 come to my mind. Michael Grant - destroyed by Lennox Lewis Audley Harrison - built up by the British press as the 2nd coming of Lennox Lewis only to fail at domestic level.
Recently, Paul Williams. And I'm counting myself in on this too. The punching machine that fought and beat Marg failed to show up against Quintana.
HowardDavis Mark Breland was a two time champ, but imo he never lived up to the hype from his amature days.