Crom Cruach is mentioned in Abdul Alhazred's Necronomicon as a lesser concubine of Shub-Niggurath. He was worshipped in Hyboria under the name "Crom". When the Hyborian age ended he was worshipped as a god in pagan Ireland. He deceived his followers into sacrificing children to him, allowing him to take their souls. Those who sacrificed to him were given the title of "Master of the Runes.
Crom Cruach's worship came to an end when St. Patrick came to Northern Ireland and discovered the pagan practices and human sacrifice. He located the cult and destroyed its idols with a hammer, before setting up Christian worship in Ireland. Thus mass worship of the Bloody Crooked One was ended.
Currently Crom Cruach sleeps beneath Stonehenge. A much smaller cult worships him still, believing him to be omniscient. It is also theorized that, rather than a concubine, Crom Cruach is in fact a facet of Shub-Niggurath due to some of his epithets (Pan, the Horned Ram) being connected to worship of the deity.