- "The dark form ran toward him with incredible swiftness. When it came near he saw that there was a kind of face on the squat ebon body, low down amid the several-jointed legs. The face peered up with a weird expression of doubt and inquiry; and terror crawled through the veins of the bold huntsman as he met the small, crafty eyes that were circled about with hair."
"The Spider God", Atlach-Nacha resembles a giant spider with a human-like face. It came from Saturn with Tsathoggua. It dwells in a cave system beneath Mount Voormithadreth, in the now extinct Arctic kingdom of Hyperborea. There, it spins a great web, forming a great bridge between the Dreamlands and the waking world. It is believed that when the web is complete, the end of the world will come.
One legend claims that he was imprisoned beneath a mountain in Siberia (but this might be one of the sundered peaks of Voormithadreth). It kills its victims by puncturing them with thousands of spins and sucking out their juices. He is subservient to Abhoth and is served by the “Grey Weavers” (who might be the Spiders of Leng). A burial ritual in the Book of Eibon references this god.
It had a cult among the Phoenicians and the Hyborians (where he was known as Zath). In modern times Atlach-Nacha is worshipped the Tcho-Tcho of the Andaman Islands and South Asia.
- In FromSoftware's video game Bloodborne there is a boss called Rom the vacuous spider, who, besides her face, looks very similar to how Atlach-Nacha is described.
- In the Doom megawad Strange Aeons, the Spinner in Darkness is revealed to be the primary antagonist, tricking the player character into traveling across the Dreamlands to free it from its prison.
- Atlach-Nacha was created by Clark Ashton Smith; it has been mentioned or elaborated upon by August Derleth, Colin Wilson, Brian Lumley, Lin Carter, Laurence J. Cornford and by some Chaosium products.