Crom Cruach (The Bloody Crooked One) is likely a giant worm or dragon-like creature. A god mentioned in Dr.Dee's Necronomicon as a lesser concubine (or facet?) of Shub-Niggurath . Crom Cruach is said to lie under Stonehenge. His cult believe him to be all-knowing. In the Hyborian Age the grim god Crom (who is probably the “public face” of Crom Crauch) was worshipped in Cimmeria. Later he was worshiped by the Celts in Ireland. It's said that its worship was ended by St.Patrick who destroyed the cult sign with a hammer. It posed as a pre-christian deity to obtain the souls of children and deceived his followers.
Sources connect Crom Cruach with Pan (which means "feeder") in ancient Greece. Also called "The Horned Ram," "Khnum," "The Lord of the Wood" (possibly this is also a name for Nyarlathotep/Ahtu?) and "Delcarnon" ("Lord of the Two Horns").
Behind the Mythos
Crom Cruach comes from Irish mythology, but was incorporated into the Mythos by Brian McNaughton; Chaosium also used the creature; Laurence J. Cornford suggested the connection to Pan and other similar gods as the public face of Crom Cruach.