This made me think of an interesting premise:

A weathered and wise yet still learning monastic sorcerer fall asleep and dreams of living a different and much darker, grimmer life. When he wakes, he is relieved for it to merely be a dream but is still changed by it. Fearing that it was a prophetic vision, he slowly becomes more and more cynical and misanthropic until even his trusting colleagues who saw him as an inseparable brother fear him to be a danger to people until they finally cast him out for his often concerning outlook and treatment of others. Now alone, the sorcerer's last tether to his former self is broken and he still haunted by his dream, sets off to reshape the world, by force if necessary, so that it may never happen. He wanders gathering power and bringing destruction to those who doubt him or his ways and violates all the taboos his former colleagues had adhered to. It continues until the sorcerer has become an abomination worse than the horrors he had dreamed of long ago. The world is now in peril all because one man grew weary of a vision and was not consoled or confronted by those around him until it was too late.

I think it sounds like a good idea for a well-meaning and totally human but severely in the wrong villain, eh?