Board Thread:Skyrim/@comment-125.35.78.90-20140318045438/@comment-29458028-20140811002504

Maybe he is an immortal necromancer from days past. You don't see him again as he went to the Soul Cairn, killed an ideal master and flee to the revenant moon.

Not exactly, but seeing as there are no family portraits, he probably has life extension, or is some new breed of vampire who decided to work for the volkihar clan for a while.