The original Damas was not a mage. While campaigning in the east, he learned some dark rituals which allowed him to indefinitely prolong his life through sacrafice and ritual self-mutilation. He is, however, an extremely good fighter and a powerfull general. Somehow he has the inate ability to turn into crows.
Between TFL and M2, he studied up and became a powerful mage, but still sticks to his mad melee skillz in combat. He's immune to the healing effects of mandrake roots, his heart is hidden away in his temple so he can never die even if his body is completely destroyed, and he can blow up the world if you give him enough time and space.
You know, I wonder why he didn't just do that in the first place, before attracting all that attention with Myrkridia and Shiver and all...