I've been thinking about starting a Dremora character that isn't allied with Mehrunes Dagon, and is bound to Mundus, but I'm not sure if it is possible. Can any one Dremora decide to not work with Mehrunes, and if so, would they need a summoner to bind them to the mortal realm? Also, would the Dremora stay a Dremora if they decided to break away from Dagon? I know there are Dremora bound to Mundus, but they usually aren't thrilled about it.

Since the Dremora are beings formed and created in the realms of the Deadlands, I would assume they are bound to Mehrunes' will.

But I suppose it wouldn't hurt to be special.

Daedric beings have changed alliances in the past, so I think a Dremora breaking away from Dagon ought to be possible. A powerful summoner would be needed to summon and bind a Dremora permanently to Mundus. Its not the most likely scenario in the book, but its your game

Dremora are not exclusively Mehrunes Dagon's servants. They haven't even always all been his servants. Yes, they can choose not to follow him. Daedra align themselves with Daedric princes to return from the waters of Oblivion more quickly after death, but Daedra can choose who they follow, or if they choose to follow anyone at all. I believe Daedra, post-Oblivion, would need a sorceror to bound them to Mundus, but I'm not quite sure about that.

Thanks for the replies everyone, I think I now have enough knowledge to continue with my idea.

There are a few Dremora who work for the Temple in Morrowind, out of respect for Vivec, and they could be said to have changed sides. There's one working for the Mages Guild as a messenger in Cyrodill. From their points of view they've maintained their honor, and honor is what makes someone kyn, or people according to Dremora. I'm not sure what the other Dremora still working for Dagon would think about it, though.

Not all Dremora work in the service of Dagon. I can't remember where I read that, but it makes sense anyway. Not every Prince has his own type of Daedroth that's unique to him.