Can someone explain what he does, and how you obtain him please?

There's a dremora butler?

Could our Dovahkiin be Mehrune's Dagon in disguise?

That would kinda be creepy.

He's a herma mora black book perk reward. He's a summon power that you can use to store gear, then he dissapears until you summon again. You get the book from Benkongerike on the North east side of the island, a little south east of the word wall with the first bound will word

Sweet, I was wondering were the last book was for me.