The Master of the Monolith is a fictional creature from Robert E. Howard's short story The Black Stone.
It was a monstrous and grotesque toad-like creature worshiped as a god by the degenerate Hungarian aborigine hybrids of fictional "Stregoicavar". An ancient and horrible thing, the Master of the Monolith was recounted as being an embodiment of all of humanity's most horrid qualities. It personified human greed, lust, and capacity for malice. The degenerate Hungarian mountain men somehow discovered and formed a cult of the monster, using a mysterious black monolithic stone found in the clearing of a mountain as a sort of altar, offering sacrifices and conducting horrible rituals to it on midsummer's nights. For an uncounted number of years, the savage people of the high mountains gave worship to the creature, crafting small idols in its image and creeping into the lowland villages to steal women and children to sacrifice; and likely would have continued, were it not for Turkish warriors come to the mountains to conquer the Hungarian people. As recorded by the Turkish Warrior-Scribe Selim Bahadur and recounted by the narrator:
...and I read, too, of the lost, grim black cavern high in the hills where the horrified Turks hemmed a monstrous, bloated, wallowing toad-like being and slew it with flame and ancient steel blessed in old times by Muhammad, and with incantations that were old when Arabia was young. And even staunch old Selim's hand shook as he recorded the cataclysmic, earth-shaking death-howls of the monstrosity, which died not alone; for half-score of his slayers perished with him, in ways that Selim would not or could not describe.
By the far future in which the Narrator comes across the Monolith, The Master of the Monolith and its beastly worshipers have long turned to dust and sit in hell, never to return. But on one occasion, Midsummer's Night, it rises from the pits of hell to bask in the veneration of its worshipers, incorporeal yet undeniably there. As the narrator states, a ghost, worshiped by ghosts.