#8 The American Bad Ass (Undertaker, Mark Calloway)
As the Attitude Era drew to a close, it was replaced by the Ruthless Aggression era. A new infux of talent from ECW and WCW pushed the physical limits of wrestling matches, and changed the business from something hokey into a more 'serious' portrayal of professional fighters.
Since The Undertaker's undead character seemed a poor fit for these new times, he was rebranded as the American Bad Ass, though he still used the Undertaker name. Basically he was a biker, with definite parallels to Stone Cold Steve Austin sans the beer drinking and middle fingers.
Undertaker actually was quite uncomfortable with the gimmick at first. He had trouble speaking as the ABA character after so many years of long pauses and cryptic speeches as the lord of darkness. Without his pyros, smoke, and magic effects, Undertaker felt like he was diminished as a performer. He also didn't care for either Kid Rock or Limp Bizkit, two flash in the pan rap-metal acts that performed his theme songs.
Ironically, it was the ABA character that led to Undertaker becoming a better wrestler. Since he was self-conscious, he worked hard to improve his in-ring game and added many MMA and submission moves to his repertoire. Taker would return to his classic gimmick, and hasn't looked back at the ABA since.