This one's easy for me. Lance Storm.
I have a lot of friends who are long time wrestling fans, mentioning Lance Storm to them causes them to cringe with disgust and describe him as the most boring wrestler in history.
Lance Storm in WCW was given the gimmick of an overly serious Canuck who could at least wrestle a tight match. WCW would eventually fold and Lance was picked up to be a member of the WWE roster.
At this time the political atmosphere of the WWE was at its zenith of unfairness and a paranoid pairing of Mark Calloway and John Layfield would actually put together kangaroo courts to haze and chastise individuals who came over from WCW as well as younger talent they felt didn't have "it".
Lance was of the attitude that Mark and John were full of shit and could go fuck themselves so he didn't attend their mock courtroom hazing ritual and warned other superstars to have the same reaction. Needless to say, Vince wasn't happy with Lance.
Lance did get a brief tag title reign and a slight push in the singles division. Then Stone Cold was augmented to rip mercilessly on Lance as a boring wrestler. I'm sure you all remember that during one of Lance's matches, Stone Cold came out and turned what could have been a decent match for Lance Storm fans into a moment where Stone Cold indulges in himself by attempting to bury a fellow wrester who has to earn a fucking paycheck too.
They then forced Lance to go out to a cheesy techno/rap theme and dance like a clown. They even made him do a spot where he tells his former tag team partner, Chris Jericho, that he actually thanks Stone Cold for showing him the light. I wanted to quit being a wrestling fan. They made a legend like Lance go out there and act as though dancing like a moron will make you a more exciting wrestler.
I posted earlier that I thought they killed Justin Credible.
There was ZERO reason why these two were denied a proper showing. They could have worked well as a tag team at WWE, just like they did in ECW.