Sekolah, the deep stalker

Sekolah is a great leviathan, the eldest of all the sea serpents, equal in power to the dragon gods Bahamut and Tiamat. Since the beginning of known time he stalked the depths of the seas across the planes of the multiverse, preying on any and all life unfortunate enough to cross his path. He created the Sahuagin to hunt the waters with him. They pay him tribute through their own hunts and conquests of other races, empowering their patron god through their own feeding frenzies.
The Deep Stalker's endless hunger to devour eventually became a threat to life across the multiverse that could not be ignored. He was exiled to Zor by an alliance of deities approximately 1000 of years ago, and quickly turned his rage against the young races of the world. His armies of Sahuagin destroyed countless cities, ships, and underwater kingdoms all across the Starlit Ocean and Azure sea before Persana and his alliance of gods intervened directly. They bound him in the deepest trenches of Zor's vast oceans, fracturing the planet in the process. To repair the planet, the deities conducted a ritual to conjoin Zor with other realms of the material plane, creating mirror versions of locations from other worlds to fill in the cracks they had created.
When they finished, they secured the seals on Sekolah through a ritual that bound him to his prison so long as his jailers exiled themselves from Zor as well. This condition upset Procan - who was native to Zor - in particular, but he accepted the terms and departed for the elemental planes.
Now Sekolah bides his time, rebuilding his armies until they are large enough to wage conquest on the rest of Zor. Even in the most peaceful , his Sahuagin are known to raid sea vessels and smaller settlements, sustaining the Deep Stalker until he can find a way to break free of his prison.
About 30 years ago, Sekolah's forces allied with the archdevil Titivilus to wage war against the people of the Azure Sea. They were thwarted by the High Seas Ass Kickers and the Saltmarsh-Lizardfolk alliance. Since then Sekolah has once again been relatively quiet.