Sheogorath

Sheogorath is the daedric prince of madness and of the Shivering Isles, a plain of Oblivion that is quite different from the others. He lives in the Palace of Sheogorath, located above the two cities Bliss and Crucible. Sheogorath tasks the player with becoming his "champion" and stopping the black march and Jyggalag from destroying his island.

Sheogorath is technically not an NPC, but a creature, namely a daedric prince, but he is not hostile, and very cheerful and friendly.