After being attacked by over 10 men in his Casket match against Yokozuna at Royal Rumble, the Undertaker vowed to return to the WWE and take revenge on those who attacked him.
Everyone in attendance watched in amazement as the Undertaker's "spirit" left the arena and would not be seen again for a few months.
Ted DiBiase, who first brought the Undertaker to the WWE, proclaimed to everyone that he had found the Undertaker and had once again brought him back to the WWE.
The "Undertaker" looked like the real thing and continued his dominance of the WWE, which had everyone convinced DiBiase was right.
However, Paul Bearer insisted that he knew where the real Undertaker was and DiBiase had brought back a fraud.
He would then challenge the new Undertaker to face his Undertaker to determine who the real one was.
DiBiase accepted and a match was made at Summerslam, where the true Undertaker made a memorable reappearance and defeated the fake Undertaker.
Video Evidence - http://www.youtube.com/watch?v=Zg8Ozd0Cl7U&feature=related