Introduction to Cthulhu Mythology

The fundamental concept of Cthulhu Mythology is that the universe is ruled by beings known as the Outer Gods, the Great Old Ones, and the Other Gods. Only few of these deities are known by name and the majority of them are both blind and idiotic, but they are all extremely powerful alien beings.

What are the Outer Gods?

The Outer Gods rule the universe and have little to do with humanity. Humans meddling with these entities usually end up mad or dead. All the races and lesser deities of the Mythos acknowledge the Outer Gods, and many worship them. The Outer Gods are controlled to extent by their messenger and soul, Nyarlathotep. Generally, the Outer Gods are thought to be unrestricted in their range and powers, and more likely to embody cosmic principles. The Other Gods include the following beings:

Azathoth: The blind idiot chaos who bubbles and blasphemes at the center of chaos (or at the center of the universe, depending on who you ask) and is thought to be the creator of all things.
Shub-Niggurath: The principle of fertility who is often named in rituals but rarely encountered.
Yog-Sothoth: A being who is one with all time and space and often appears as a cluster of floating, iridescent spheres. It is coterminous with all time and space, but locked somehow outside the mundane universe.
Nyarlathotep: The soul and thousand-formed messenger of the Outer Gods. Most Mythos beings are indifferent to humanity, but Nyarlathotep is more of a trickster who enjoys giving humanity the key to its own destruction.

Who are the Great Old Ones?

The Great Old Ones are not as supernatural as the Outer Gods, but they are nonetheless god-like and terrible. Humans are much likely to worship Great Old Ones, who are comparatively near at hand and who occasionally participate in human affairs or contact individual humans, than they are to worship Outer Gods. Beings serving the Great Old Ones frequently inhabit the remote vastness of the Earth. Humans most often encounter the worshippers of The Great Old Ones and their alien servants. Each Great Old One is independent of the rest, and many seem to be temporarily imprisoned in some way. But it is said that "When the Stars Are Right" the Great Old Ones will be freed from their imprisonment and they will rule the world once again. When the stars are not right, they cannot live. "Cannot live" need not mean dead, as the famous couplet from the Necronomicon suggests...

"That is not dead which can eternal lie, And with strange aeons even death may die."

One trait of most Great Old Ones is a limitation on their influence. Cthulhu is imprisoned beneath the Pacific Ocean in the city of R'lyeh, Ithaqua the Wind-Walker is confined to the far north of our planet, and so forth. Even those Great Old Ones less able to act may reach out and talk in their dreams to humans, who learn to revere these beings. The Great Old Ones are often worshipped on Earth by insane human cultists and other species; Cthulhu himself is served by humans, the amphibious deep ones, and his own spawn.

Cthulhu is perhaps the most "famous" Great Old One. With the rest of his race he sleeps in a vast tomb at the bottom of Pacific Ocean. But when the Stars are right the Lord of R'lyeh will rise from his watery grave and rule the world rightfully once again. Cthulhu seems to be the most important Great Old One on Earth. Hastur the Unspeakable dwells near Aldebaran, and Cthuga near Fomalhaut.

Aside from Cthulhu, these are some of the most well-known Great Old Ones:

Cthugha: It appears as a large ball of fire, and is often accompanied by smaller beings called "fire vampires" or "flame creatures". Cthugha may only be summoned when Fomalhaut is in the sky.
Dagon: A Canaanite god of agriculture worshiped by the Philistines and whose priests opposed those of Yahweh (see 1 Samuel 5:1-6). As a result of an error made by the fourth-century scholar St. Jerome and the find of a merman depiction near one of his temples, people thought that Dagon was a fish-god.
Glaaki: A creature which dwells beneath a lake near the Severn River. It has a slug-like body with stalked eyes and spines, and commands a horde of undead servitors.
Hastur: An "air-elemental" who is Cthulhu's "half-brother" (whatever that means).
Ithaqua: This creature is the "windigo" from Cree and Ojibwa mythology, a cannibalistic giant with a heart of ice.
Nyogtha: Also known as the Thing that Should Not Be, Nyogtha is a black amorphous mass that dwells beneath the ground. He was worshiped by one of the witches at Salem.
Shudde M'ell: A slug-like being with tentacles where a face should be. Shudde M'ell spends much of its time in Africa, and is the leader of the underground species called the cthonians.
Tsathoggua: A god resembling a furry toad, Tsathoggua dwells in the cavern-world of N'kai. Tsathoggua occasionally eats visitors, but is more likely to be asleep when encountered.
Yig: This Great Old One appears as a huge snake-headed man. He cares little for humanity, but brings terrible vengeance on those who attack snakes.

Who are the Elder Gods?

A group of independent beings who oppose the Great Old Ones and Outer Gods. The most famous of these is Nodens, Lord of the Great Abyss. There are others, such as Kthanid and Bast (from Egyptian mythology); but they generally avoid becoming involved in human affairs and so their true number and names remain a mystery.

What are some of the major non-human species in the Mythos universe?

Particular species are often associated with Great Old Ones or Outer Gods - byakhee with Hastur or nightgaunts with Nodens. These are servitor species who help their masters by frightening of humans or by acting as assassins, messengers, spies or agents. These are much lesser species than their masters but most of them are still too terrible to even be seen by pitiful humans. Other alien races are also important, and sometimes have been even able to hold their own against the Great Old Ones. The independent races vary in power and some are extinct. They are intimately connected with our world

At the dawn of the Cambrian age, beings known only as the elder things flew to the Earth. They inhabited much of the land, warred with other species, and finally were pushed to Antarctica. The elder things, perhaps mistakenly, bred organisms eventually to become the dinosaurs, mammals and humanity. They also bred the horrible shoggoths, whose ultimate revolt led to the semi-extinction of the elder things.

Also many other races such as Fungi from Yuggoth, Great race of Yith or Star spawns of Cthulhu inhabited the Earth before the rise of humanity. At the present humans share the planet with deep ones, ghouls and with a handful of mi-go. Other species occasionally visit the Earth, or are sleeping or are dormant.

Here are some of the more known species:

Byakhee: Winged creatures which dwell in the depths of space near Aldebaran. If a ritual involving a magic whistle and a fluid called "space-mead" is performed, a byakhee will appear and serve as a mount for the caster. They are allied with Hastur.
Deep Ones: Undersea dwellers which look like a cross between humans and fish (or frogs). Deep ones sometimes breed with humans, creating offspring which are human at first but make a slow transformation into deep ones. The deep ones serve Dagon and Cthulhu.
Elder Things/Old Ones: Starfish-like entities which are part animal and part plant. They came from the stars in ancient times, from another place in the galaxy within this space-time continuum, and absorbed chemicals that made them do without breath, eating and heat, but lost this ability late in their history. In the beginning they lived under the sea in the Antarctic Ocean, but later migrated to land. For food purposes they started life on earth, All life on Earth from bacteria to Dinosaurs to Humans are a result of their genetic experiments. They made multi-cellar protoplasmic masses named Shoggoths (see below), which they used as slaves. They battled different cosmic enemies on earth. Spawn of Cthulhu came from the stars warred with the Old Ones. They settled peace, and shared the land. The spawn of Cthulhu's biggest city was R'lyeh, it later sank in pacific ocean due to geologic activities. Again the Old Ones were attacked from outer space by the Mi-Go. They eventually abandoned their Antarctic city to live underwater, and found a large underground ocean, The Stygian. They build a great city at the bottom. The Shoggoths tuned against them and destroyed their civilization. It is unknown whether they have become extinct.
Great Race of Yith/Yithians: Time-traveling beings with no true physical form, they occupied the bodies of immense iridescent cone-shaped creatures millions of years ago. The creatures had long arms with pincers, a trumpet-like mouth, and a small round head. Members of the Great Race can send their minds into the future and swap consciousnesses with dwellers there. They usually do so as a part of their research, but at times they travel en masse in conquest.
Hounds of Tindalos: Creatures which dwell in the distant past. They are not a threat unless they sense a time-traveler, in which case they hunt the person down and kill them. They manifest themselves through angles, and cannot enter an area in which all surfaces are curved.
Mi-go/Fungi from Yuggoth: Crustacean-like fungus beings which have an outpost on Yuggoth, or Pluto. They come to our world to obtain precious minerals and for other dark purposes, though they try to remain hidden. They serve Nyarlathotep and Shub-Niggurath at times, but often seem independent in their motivations.
Serpent People: Millions of years ago, the serpent people were mighty sorcerers and scientists who ruled vast empires. Today, they hide from humans through magic and isolation. Their degenerate descendants were the inspiration for the myths of the faeries, or "Little People". They do not serve any one god, but seem to favor Yig.
Shoggoths: Huge protoplasmic beings able to take on any form. Shoggoths were made from multi-cellular protoplasmic masses by the Old Ones. They were used as slaves, and controlled via commands induced via hypnotism. Shoggoths are very strong, and totally unaffected by cold. Later they were able to change themselves physically, and grow limbs. In time they managed to grow a brain, and a mind of their own. This made them hard to control. They were 15 foot in diameter consisting of a viscous jelly which looked like an agglutination of bubbles. described as: "Formless protoplasm able to mock and reflect all forms and organs and processes - viscous agglutinations of bubbling cells - rubbery fifteen-foot spheroids infinitely plastic and dilute - slaves of suggestion, builders of cities, growing intelligence". They produced a musical piping: "Tekeli-li!", mimicking the Old Ones. They later on battled the Old Ones, and when an Old One was killed, he was covered in slime, normally with his head missing. The Shoggoths communicated with the Old Ones via musical piping, but the Shoggoths were almost uncontrollable in the end. After their rebellion against the Old Ones, most of them were destroyed. A few may be found in the Elder Things' former cities, or working with the deep ones.
Star-spawn of Cthulhu/Cthulhi: Beings which appear as smaller versions of Cthulhu. Most are imprisoned at R'lyeh, but some may still be free.