5. Ministry of Darkness (1999)
How do you make The Undertaker even more diabolical? Have him start a deadly cult, speak in demonic tongues, and attempt to take over the WWE, that's how!
The Ministry of Darkness persona had been teased ahead of 1999, but it was in January of that year that it fully went into action as a return from The Phenom kicked the Ministry's reign off. And it was a truly captivating experience watching him get to play this evil heel character for the first time in years. He was ruthless and that came across in his in-ring action too, as he would resort to some shady and violent methods to teach his opponents a lesson.
As far as strength goes, it was a bit of a mixed bag with the Ministry persona. He was incredibly strong in its early days and he always remained strong in his character, but the booking wasn't always right. When he was the WWE Champion, he was booked well, but outside of that, the Ministry was booked stronger as a whole than he was. And throw in the fact that Calaway was suffering from some real life injuries during the time (which eventually limited his in-ring work until his return in 2000), he wasn't at his strongest physically, either.
That being said, there is a reason that he was the all-powerful leader of the Ministry of Darkness, and I certainly won't argue with that. Also, he never looked more powerful than he did when he was sitting on his dark throne during those vignettes in that hooded robe.