Occipitus is the 507th layer of the Abyss. Formed of a portion of Celestia that was cast down to the Abyssal realms. Formerly the realm of Adimarchus, demon prince of madness, tentative control of the realm is now shifting into the hands of one Aeduin Tharn.

Aeduin has taken the partial mantel of Adimarchus upon himself and is bonding himself to the plane itself. Once a bard and warrior, Aeduin was changed when the bonding began. More than once dying and returning to that plane, the last time he was changed forever. His bonding with the plane reached a level where he could now channel its energies. He became a cleric, channeling the divine energies of the plane into helping his companions to save the city of Cauldron.

Once Cauldron was secured he returned to Occipitus to shape and guide its future. With the aid of his senechal, a hezrou demon named Nebatheron, he is creating a world where all who are outcast will be welcomed.

He was further aided in his goal when the wandering Inn Between Worlds appeared on the plane of Occipitus. To its proprietor, he offered a permanent location for the inn and now it sits upon the planes of dust, opening doorways into every plane of existence.

Occipitus wiki