The Undertaker has never been defeated at Wrestlemania and never will despite all the speculation. It is in The Undertakers contract that he cant lose on the grandest stage of them all.
This stipulation wasn't in his contract until after his third victory at Wrestlemania. Taker has hinted at his retirement after his 20 - 0 at Wrestlemania, the ideal retirement would be after his 25 - 0 25th anniversary victory however The Undertaker is looking at retirement soon. it is wrestlemania 27 the last year for the undertaker, triple h and the undertaker are retiring and triple h is going to break the streak 18-01 that one is triple h. they are going to fight in the last wrestlemania for them to either brake the streak or keep it
The Undertaker has never been beaten at WrestleMania. His streak at the moment is 19-0 and counting.