So i just fought this ridiculous Dragon Priest on master, toughest enemy I have faced in the game yet, bosses included. I was wondering, is there a backstory for such a powerful enemy?

I was a vampire and needless to say, his fire attacks were almost killing me with every shot. another question, what was the overpowered fire attack he constantly spammed? Was it a supercharged firebreath?

There's a book called Ahzidah's Descent. Apparently he only joined the priesthood for their power and may have been the first human to master elven sorceries.

Him and the other dragon priests on Solstheim are quite a challenge, and he is one of the few with a back-story . I don't know what that fire spell was though.

He was probably using a normal fire spell, but it was super charged by his mask which adds 25% damage to fire spells.

Hardest for me was Dukaan.....holy **** that frost spell....

Ahzidal and Vahlok was hard enemys!

On adept they were easy, needless to say just secret of arcana for 30 seconds spam stunning fireballs with my dremora lord holding of the draugr.