The slippery grey-white creatures who came in black galleys from the dark side of the moon and conquered Leng and its people. These horned, hoofed, and wide-mouthed almost-human creatures ply their unearthly rubies along the coasts of Dreamworld taking only fat slaves and gold in return. It is believed the High Priest of Dreamworld at the remote monastery on the Leng Plateau is one of these creatures. Carter and Pickman the ghoul joined forces to battle the moon-beasts.
An early story Lovecraft wrote may have been the inspiration for the moon-beasts. In a letter to Kleiner from Jan. 20, 1916, Lovecraft said, "Regarding early reading, when I was about twelve I became greatly interested in science, specialising in geography (later to be displaced by astronomy), being a Verne enthusiast. In those days I used to write fiction, and many of my tales showed the literary influnce of the immortal Jules. I wrote one story about that side of the moon which if forever turned away from us-using, for fictional purposes - the Hausen theory that air and water still exist there as the result of an abnormal centre of gravity in the moon. I hardly need add that the theory is really exploded - I even was aware of that fact at the time - but I desired to compose a 'thriller'."
("The Dream-Quest of Unknown Kadath")