From DreyNet

At one time, Remorrah was a friend and peer to Arthur. He struck a deal with the Otherdarken in order to protect his worlds, betraying Arthur in the process. Now the Otherdarken cannot touch the worlds of Remorrah and only seek after Arthur’s worlds.

The experience tainted Remorrah’s mind and he became twisted and fey, removing himself from his creations to brood in a dark corner of existence.