The Cthulhu Mythos is a collection of works of the writer Howard Pillip Lovecraft and his friends, concerned with a pantheon of godlike aliens and the miniscule place of humanity in a bleak and uncaring universe.

Cthulhu is not actually the main figure of the mythos, having only one story devoted to him. The mythos was actually originally known as "Yog-Sothothery."

Pantheon:
-Azathoth: A blind, mindless god that dreamed up reality. Served by a legion of amorphous creatures playing an eternal lullabye on flutes and drums.
-Yog-Sothoth: The gate and key of knowledge and the souls of every living thing.
-Cthulhu: God-King of the Star Spawn. Cousin to Yog-Sothoth.
-Hastur: He Who Must Not Be Named. Ex-boyfriend to Shub-Niggurath. Patron of the Byakhee. Easy to conjure and enjoys a good play.
-Shub-Niggurath: The Black Goat of the Woods with A Thousand Young. Patron of group sex, forests, and group sex in forests. Yeah, she's fun at parties as long as the snacks hold out and you're willing to put up with all those kids of hers.
-Nyarlathotep: The Soul and Messenger of the other gods, and the cosmic version of a mean kid with a magnifying glass lazering ants to death. Has a thousand faces and is an asshole in all of them.
-Dagon and Hydra: God and goddess of the ocean. Patrons of the Deep Ones, hideous fish-people.
-Tsathaggua: A froglike god of gluttony. His servants exist only to bring him food since he's such a lazy fuck he won't get off the divine couch.

Elder Races:
-Byakhee: servants of Hastur, they resemble a soggy biscuits between a rotting corpse, an ant, a bat, and a vulture.
-Mi-Go: Insectoid fungi. Despite being sexless, worshippers of Shub-Niggurath.
-Star-Spawn: Cthulhu's children and worshippers.
-Elder Things: Plantlike aliens living in Antarctica.
-Yith: The first creatures to have evolved on Earth. Possessed en masse by a horde of psychic aliens.
-Shoggoths: Huge amoebas used by the Elder Things as construction equipment. Once they evolved sapience, they were very upset.
-Deep Ones: Humans touched by the influence of Dagon and Hydra. They are immortal, fishlike, and amphibious.

Creatures of Sorcery
-The Worms that Walk: Undead human sorcerors whose souls and consiousness infuse the vermin who feasted upon their flesh, controlling them as they did their old bodies. They resemble either a mass of worms in human shape, or a single, huge, anthropomorphosized maggot.
-Zombies: The undead slaves of a magician, although they can be produced as the byproduct of a mental transfer ritual.

Dreamland Denizens:
-Ghouls: Hoofed canoid creatures that eat dead bodies.
-Nightgaunts: Faceless demons fond of tickle torture. Like ghouls, they eat corpses.
-Leng Spiders: Giant spiders that can reach several tons in body weight. Hate the Men of Leng
-Men of Leng: Wingless demons in Arabian getup. They hate the leng spiders right back.
-Dholes: Photophobic creatures resembling giant worms. Live in pits filled with bones.
-Cats: Your everyday housecat. The most benevolent of the Mythos entities. In the Dreamlands, they can speak.
- Moon Beasts: Elephantine creatures who live in the moon's swamps (less metaphorical in the Dreamlands.)
-Humans: Human beings. Good, wholesome, upstanding folk often go irrevocably insane upon meeting anything more powerful than a dreamlands creature. Some humans are psychic and able to live comfortably in the Dreamlands indefinately, up to and including many strange aeons of their own.