Jyggalag

Jyggalag is the main antagonist of The Elder Scrolls IV: Oblivion: Shivering Isles. He is the Daedric Prince of Order, in a bad way, i.e. boring and lifeless. In days of old, he and his Knights of Order ruled over an ever–expanding empire of “perfect” order, and the other Daedric Princes hated him so much because he was so boring and was making more of the universe boring, that they cursed him to become Sheogorath, the Prince of Madness, who is the exact opposite of Jyggalag, and replaced him as a prince in mortal worship, which is why Jyggalag was never mentioned in any of the games before Shivering Isles.

Once at the end of every era, Jyggalag would be allowed to become himself again and take over and destroy the Shivering Isles in an event known as the "Greymarch", which was always successful since Sheogorath wasn’t there to defend his realm, as Sheogorath was Jyggalag, but sometime afterward Jyggalag would turn back into Sheogorath again and the process would be reversed and start over.

During the events of the game, Sheogorath invites the player into his realm to be his champion and stop the upcoming Greymarch, and when the Greymarch does happen the player ultimately fights and destroys Jyggalag. Jyggalag’s spirit then appears and tells the player that by defeating him, they have broken the cycle and he can now be an actual Daedric Prince again, while the player becomes the new Sheogorath.