DAGOTH UR DAGOTH UR DAGOTH UR DAGOTH UR DAGOTH UR DAGOTH UR DAGOTH UR DAGOTH UR DAGOTH UR DAGOTH UR DAGOTH UR DAGOTH UR DAGOTH UR DAGOTH UR DAGOTH UR DAGOTH UR
That's Dagoth Ur, the primary antagonist of The Elder Scrolls III: Morrowind. He's kinda an undead god-king thing... Except he isn't, because the metaphysics of the in-game setting are kinda screwy like that. Technically, he isn't undead so much as he's anti-alive. Even that's a sloppy explanation.
Anyway, he was the player character's bro in a past life and it's the player's job to "kill" him, whatever that even means.
Anti-alive in a similar manner to D&D undead?
Nope. That'd be regular undead. Dagoth-Ur is an entirely different thing altogether.
In The Elder Scrolls, when you die you go to a plane called the Dreamsleeve, where you experience whatever afterlife you believed in until you reincarnate. This is also where you go when you sleep, which is why you dream. When you're awake, you're in the material plane, or Mundus. So if you're alive, you can occupy one of two states:
Alive, Awake in Mundus(AlAwMu)
, or Alive, Dreaming in the Dreamsleeve(AlDrDS)
Now, undead do exist, but the way necromancy works in The Elder Scrolls is that the dead are awakened from their rest in the Dreamsleeve, bringing them back to Mundus in the service of the caster. This means the dead can occupy two possible states:
Dead, Dreaming in the Dreamsleeve(DeDrDS)
, or Dead, Awake in Mundus(DeAwMu)
Dagoth Ur occupies none of these states. He was killed millennia ago, quite thoroughly, but due to shenanigans involving the heart of a dead trickster god, Dagoth Ur is actually solipsistically dreaming his own presence in Mundus.
As such, he is Dead, Dreaming in Mundus(DeDrMu)
. This is impossible.