|Tarnhem imprisoned within a crystal vessel. From Return to the Tomb of Horrors.|
Tarnhem stands twelve feet tall with dark red skin, leathery wings, and clawed hands and feet. His face is fanged and demonic.
Tarnhem is the father (and, currently, the slave) of Acererak.
Tarnhem's Abyssal layer, called Noisome Vale, is covered in volcanic vents and cut by a ravine full of writhing worms. The worms inhale the acidic gas that suffuses the layer and exhale breathable air, which allows mortals to survive the atmosphere as long as they remain near the ravine of worms. Tarnhem's manor is on the edge of the ravine, but the constant whisperings of the worms can be maddening. His manor is still maintained by Tarnhem's servants, though Tarnhem himself hasn't been seen since his disappearance over 800 years ago. Currently, the marilith Kaon claims rulership of the layer in Tarnhem's name by keeping control of the Seat of Grubs, though this claim is known to be spurious by all who dwell in the manor.
Long ago, Tarnhem was summoned by a conjurer who could not hope to control him. After devouring the wizard, the demon raped his servant girl, impregnating her with the fetus that would later be named Acererak.
When Acererak sought to transform himself into a lich, one of the prerequisites for the ritual was that he knew his fiendish father. After much arcane research, the cambion learned the demon's true name, Maasgheldur, and used it to bind him into servitude. He has never forgiven Tarnhem for the fiend's treatment of his mother, and took glee in enslaving his mother's rapist. Through his mastery of Tarnhem, Acererak controls hordes of demons who helped him build his works and maintain constant vigilance over the Tomb of Horrors and Acererak's other properties to this day.
Tarnhem tries to betray his son in the course of the events of Return to the Tomb of Horrors, and in revenge Acererak coldly attempts to kill him.
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