Chthon appeared in 1975 Marvel Comics called Marvel Chillers.
Chthon is one of the Elder Gods of Earth and the planet's first master of black magic. Like his brother Set, Chthon degenerated into a demon and was forced to flee the Earthly plane due to the Demogorge. He wrote the Darkhold to serve as the link between the Earth and the Flickering Realms to which he escaped.
Chthon and his worshipers, the Darkholders cult, sought to return the Elder God to Earth. He created many demonic races to serve him, including the N'Garai, Ape Lords, Man-Bats of Ur-Xanarrh, Harpies, Goblins, Troids, Broodlings of Chthon, Nightgaunts; and his magics were used on Earth to create the Werewolves, Vampires, Zombies.
One of Chthon's schemes involved bestowing an infant girl in Wundagore Mountain with the latent ability to use chaos magic so that he could use her as his future vessel. That girl grew up to be Wanda Maximoff, the Scarlet Witch. This plan ultimately backfired as the Scarlet Witch eventually used Chthon's own Darkhold against him to seal him into herself.