The Watcher of the Mists
Zon-Kuthon, the Midnight Lord, is the god of Envy, Pain, and Loss. His followers generally enjoy pain— either inflicting it on others or experiencing it themselves (or both). Most worshipers of the Midnight Lord are heavily scarred as a result. There is no centralized church of the Midnight Lord— priests are pretty much left to their own to spread pain and despair through the world. As a lawful faith, however, priests tend to organize worship independently on the local level, and many independent cults have their own hierarchies and traditions. Temples of the Midnight Lord are essentially torture chambers, where the faithful hear the words of their god whispered through the screams of their victims— both willing and not.
While not a bookish faith, the holy text of Zon-Kuthon is a short work called The Umbral Leaves. Copies tend to be made of parchment from human skin and written in human blood. The language of the text is Infernal.