Cthulhu Mythos

"Climbing from the depths abyssal

To give mankind its dismissal,

Soon will come the Great and Dreaded Old Ones!

To destroy mankind, the bold ones

Come at last the long foretold ones

'Til o'er all the world they reign, the world they reign!"

"Yog-Sothoth or mankind's blunder

Soon will tear the veil asunder!

Iä! Iä! Cthulhu fhtagn!

Nylarlahotep, Crawling Chaos

Comes from Azatoth to slay us!

Soon the Old Ones come again!

P'raps we'll summon up a Shuggoth;

Find our brains on distant Yuggoth!

Soon the Old Ones come again!"

- From "Climbing from the depths abyssal", a Filk of Gilbert and Sullivan's "Climbing over rocky mountain" by Adam Cuerden.

An informal and, appropriately, chaotic Shared Universe that squarely defines the darkest and edgiest of genres, cosmic horror. It was started unintentionally by HP Lovecraft and his circle of peers (informally called the 'Kalem Club') who belonged to the embryonic Fandom, at that stage less about Speculative Fiction but more about writing short amateur "weird" stories for the 'pulp' magazines, at least for Lovecraft.

Lovecraft had already incorporated small elements of Robert W Chambers' earlier The King in Yellow and the writings of Arthur Machen by way of Shout Outs, and as time went on, Lovecraft and his friends began referring to his Eldritch Abominations and Tomes of Eldritch Lore in their writings, though usually not actual characters, and to share references made in his friends' stories or private letters. Mythopoeia defined the abstract, and original, cosmic setting.

The actual term Cthulhu Mythos, depending on how you define it, post-dates Lovecraft's death, at which time H. P. Lovecraft's work got seized and expanded on by August Derleth. Lovecraft called his budding mythology "Yog-Sothothery".

Due to the Shared Universe's informal nature there have arisen several rather divisive conceptions of the Mythos, generally categorized as the Lovecraft purists' version; the version including the broad post-1930s expansions by later writers like August Derleth (who is a controversy unto himself) and Ramsey Campbell; and then there's the rigidly codified and de-mystified Tabletop RPG adaptations which crunch down Mind Screwdriver-style to produce orderly game rules from an inherently disorderly canon. Information from the latter has tended to proliferate across the Internet disproportionately, resulting in simple Google searches producing a majority of pages derived from the game and its various campaigns, which are not always labeled as such.

HP Lovecraft has his own trope listing, so tropes here should be for tropes that are not specific to his work, or have been greatly expanded from his work. See also Cosmic Horror Story (for works which deal with Lovecraft's themes [and, optionally, make use of the Mythos) and Lovecraft Lite for works that take Lovecraft and Mythos less seriously.

See also the Call of Cthulhu RPG

Sub-settings within the Cthulhu Mythos 'verse include:
 * Lovecraft Country: Lovecraft's own setting; Arkham, Dunwitch, Innsmouth, and Kingsport, and anywhere nearby that fits the imagery.
 * Campbell Country: Any Mythos-derived setting in Europe, most often England. The old castle from HPL's The Rats in the Walls and Ramsey Campbell's Severn Valley region are ideal examples.
 * The Dreamlands: Fantastical world created by people's dreams, focusing more on the surreal than terror.
 * Delta Green: The Mythos meets government conspiracies and black ops.
 * Hyperborea: Prehistorical Greenland before the ice age. Created by Clark Ashton Smith, it focuses more on the weirdness than horror.
 * Kull, Conan the Barbarian, and Bran Mak Morn: Robert E Howard's works form a peripheral part of the Mythos - the stories tend to be human-centric. "The Tower of the Elephant", one of the best early Conan stories, features a Lovecraftian abomination.

Notable Cthulhu Mythos writers include:

 * The "Lovecraft Circle" : The original writers who corresponded with each other and used the elements of the mythos in their writings.
 * August Derleth. Co-founder of Arkham House, and proponent of the Mythos. Also see The Trail of Cthulhu.
 * Clark Ashton Smith.
 * Donald Wandrei. Co-founder of Arkham House.
 * HP Lovecraft. Obviously.
 * Henry Kuttner.
 * Frank Belknap Long.
 * Fritz Leiber
 * Robert Bloch.
 * Robert E Howard.
 * Pre-Lovecraft Authors : Writers whose works were before Lovecraft started, but were a great influence on him. Latter retconned into the Mythos:
 * Ambrose Bierce: Created the lost city of Carcosa and the name Hastur, which reappear in The King in Yellow.
 * Lord Dunsany: Inspired Lovecraft's dream-prose period and the idea of creating a pantheon of his own.
 * Robert W Chambers: Wrote The King in Yellow, which was a great inspiration for Lovecraft, and was, in turn, inspired by Bierce.
 * Arthur Machen: Wrote The Great God Pan, inspiring Lovecraft's take on Half Human Hybrids, especially in "The Dunwich Horror".
 * Brian Lumley: Whose Titus Crow, Primal Land, and Hero of Dreams forms a part of the mythos.
 * Chiaki Konaka, who has written several Mythos stories in addition to his work as an anime screenplay writer.
 * Lin Carter: The major scholar and archivist of the Mythos, as well an editor and writer.
 * Ramsey Campbell: Notable for founding Campbell Country.
 * Stephen King: Contributed a couple of stories set in the Mythos.
 * Thomas Ligotti: More influenced by Lovecraft's bleak philosophy than by the particulars of the Mythos, but has written a few explicit homages like "The Sect of the Idiot."


 * Affectionate Parody: Several, including:
 * The aptly named Cthulhu Saves the World is a huge love letter to both 16 bit RPGs and to the Mythos as a whole.
 * The Unspeakable Vault of Doom
 * "Love's Eldritch Ichor" by Esther M. Friesner is a silly love story between a harried publisher and a romance writer, a descendant of Lovecraft who is protected by Cthulhu.
 * Pokethulhu, crossing the mythos and Pokemon.
 * Hello Cthulhu
 * Nyarko San, a romantic-comedy which features Nyarlathotep as a Moe, hyperactive schoolgirl.
 * Alien Geometries: One of the most notable examples being on the island of R'lyeh, in "The Call of Cthulhu".
 * Aliens Are Bastards: Just about everything not of this Earth is evil and/or horrifying. About the only exception are Elder Thing and the Great Race of Yith, who still do freaky things like body-swapping with humans so they can visit Earth, and politely mind-wiping the unfortunate human when they switch back.
 * Ancient Astronauts: In addition to Lovecraft's Cthulhu, Elder Things, Mi-go, Yithians, and Flying Polyps, later writers added the Shan, Star Vampires and Yuggs.
 * Another Dimension: Were Cthulhu and the Mi-go originated. Also the Dreamlands.
 * Apocalyptic Log: Often found by investigators, and some stories are entirely these.
 * Artifact of Doom: Plenty, but the Shining Trapezohedron is probably the most noted. Also an Artifact of Death, if you differentiate between the two.
 * Asshole Victim: A common occurrence. Though, the reader may feel some pity towards some because of how nasty their deaths are.
 * Author Avatar:
 * An unusual example is that Lovecraft himself became a figure in his own mythos and was written into several stories by other authors, either as an avatar or even more curiously as himself. In addition to this, the first Lovecraft short story collection The Outsider and Others, put together posthumously, was inserted into the mythos as one of the arcane tomes frequently referenced in the stories of other authors.
 * Robert Bloch killed off a character based on Lovecraft in "The Shambler from the Stars"; in response, Lovecraft killed off a character based on Bloch in "The Haunter of the Dark".

And then Bloch wrote a sequel which mentions both to the Expies and to himself and Lovecraft. You would think that Bloch or Blake would have realized that they were carbon copies of each other down to having written almost identical stories. To top it off, the main character (Fiske) is also an avatar, as Bloch wrote under a pen name of "Tarleton Fiske".
 * Frank Belknap Long had another character based off Lovecraft in "The Space-Eaters".
 * The main character of Fritz Leiber's "Terror from the Depths" shares many similarities to Clark Ashton Smith.
 * "HPL" by Gahan Wilson even has Lovecraft (and Clark Ashton Smith) as summoners of Mythos entities.
 * Lovecraft himself had several avatars: Ward Phillips, Randolf Carter, and Abdul Alhazred (which was Lovecraft's childhood play name).
 * T.E.D. Klein's Black Man With A Horn has a character based off Frank Belknap Long.
 * Bizarre Alien Biology: Almost all the aliens in the mythos have this. There's fungus-crab-bat things, Crinoid/plant lifeforms, giant shape-shifting amoeba-like monsters, and giant telepathic squid-worms. And that's not getting to the Great Old Ones, who aren't even of normal "matter".
 * Blue and Orange Morality: An alternative take on the Mythos by some authors. Most of the beings in the Mythos are beyond good and evil, as we understand it. For example, Long presents the Hounds of Tindalos as "Foul" and "descended of angles". Humans are somewhat "Pure" and literally descended from curves. In "A Note on the Cthulhu Mythos", Derleth explains that the entities of the Mythos are "beyond mundane morality".
 * Canon Welding: Very common.
 * City With No Name: "The Nameless City".
 * Covers Always Lie: Lovecraft anthologies (such as the Del Ray ones) tend to have weird, surreal imagery that often doesn't have anything to do with anything in the stories. Though, it does communicate the atmosphere of the books well enough.
 * Cults: The Mythos is filled with Old One worshipers with horrible rituals. They range from the Arkham Witch Coven, various madmen like the Whateleys, The Brotherhood of the Yellow Sign, and the English Temphill Cult to name a few.
 * Cultural Cross Reference: Mythos references have been made in Japan - some subtle (Big O, Digimon) and others outright (Haiyore! Nyarko-san).
 * Dark Fantasy: Really Dark.
 * Death By Adaptation: in the 2005 silent film adaptation of The Call of Cthulhu. 
 * The same goes for a bunch of other characters in The Whisperer In Darkness as well. Most prominently,.
 * Did You Just Romance Cthulhu?:
 * Lovecraft's "The Dunwich Horror". Yog-Sothoth mates with a human woman
 * Michael Shea's "Fat Face". An "escort" seeks comfort from a large, seemingly kindly man.
 * Played with Ramsey Campbell's "The Faces At Pine Dunes". The protagonist and his girlfriend is investigate his parents' strange behavior.
 * The Dreaded: Most of the monsters don't need to kill you to disable you. They can do that just by looking really really scary. The Cthulhu Mythos is the Trope Codifier of Eldritch Abomination for a reason.
 * Dug Too Deep: Happens in a Lumley tale
 * Eldritch Abomination: For all practical purposes, this is the font and origin of all blobby god-things with unpronounceable names.
 * Eldritch Location: Lots and lots.
 * Fantasy Pantheon
 * Fictional Document: The various unspeakable books, commentaries on said books, as well as the various final testaments.
 * Fish People: The Deep Ones and their Half Human Hybrids, obviously.
 * Genocide Backfire: The Doom that Came to Sarnath.
 * Go Mad From the Revelation: Trope Namer.
 * Half Human Hybrid: And not the cute furry kind, nor the sympathetic outcast kind.
 * He Knows Too Much: Whoever finds out too much about the Mythos (such as the Cthulhu Cult) tend to be hunted down and killed. That is, if the person in question doesn't go insane first or get eaten.
 * Historical Domain Character: It's common for Mythos stories by later authors to feature Lovecraft himself as a character, often with the premises that he wrote truth disguised as fiction. Lovecraft Is Missing is a prominent example.
 * How We Got Here: Typically of the "See, this is why I must commit suicide before sundown..." variety
 * Human Sacrifice: Wither it's being used in some unspeakable experiment/ritual or just being a snack for a ''Old One", it's very common.
 * I Have Many Names: All of the Great Old Ones and other incomprehensible beings have multiple aspects and/or names. Part of this is due to multiple attempts at spelling a alien word (Cthulhu, Ktulu, Clooloo, Q'thulu, Tulu, etc.) and partly just due to the use of epithet (Nuclear Chaos or The Daemon Sultan for Azathoth) in the case of The Scottish Trope where the true name is forbidden (even "Azathoth" is a pseudonym).
 * Insectoid Aliens: The Mi-Go and the Insects From Shaggai.
 * Loads and Loads of Races: HPL himself mentioned or sometimes showed a few dozen aliens and monsters, and subsequent authors and co-writer have expanded this greatly. That's not even getting into the godlike deity-aliens.
 * Lovecraft Lite: The stories by Smith, Derleth, Lumley, and Howard in particular. Smith is more due to the focus on the weirdness, and Howard's characters were simply Badass enough to face cosmic horrors and fight them. Even Lovecraft had some lighter tales.
 * Naturally, the Mythos parodies and homages tend to be this as well.
 * Masquerade: One of the defining aspects of the Mythos, living in ignorance of the true horrors of reality.
 * Medium Awareness: Lovecraft encouraged the authors he corresponded with to use elements of his mythos in their stories, even if those stories were not part of the mythos itself. This emergence of common elements in seemingly unrelated works of literature created the impression that the mythos was actually real, thus leading to the fan theories that Lovecraft actually had encounters with eldritch entities. This culminated in a peculiar case when an infamous Moral Guardian by the name of Patricia Pulling included in a questionnaire submitted to police as a means of investigating people for possible occult affiliations, a question regarding whether or not the suspect had heard of and read the Necronomicon. This question, among various other things, led to her discrediting as a credible expert in the area of occult crime.
 * Moe Anthropomorphism: You can find most, if not all, of the mythos beings depicted as human girl. Cthylla is notable that, being called Cthulhu's daughter, it's much easier to search for her moe art than squid-like form. Nyarko San takes this to the next level, with Nyarlathotep, Cthugha, and Atlach-Nacha as cute Moe girls.
 * Mushroom Man: The Fungi from Yuggoth.
 * Names to Run Away From Really Fast: Pretty much all of them, unsurprisingly.
 * No Hugging No Kissing:
 * Lovecraft's stories contain virtually no hanky-panky. His narrators are universally chaste. Females characters are consistently abominations in disguise. On the very rare occasions that sexual activity is implied, it is depicted negatively and guaranteed to result in inhuman hybrid demon spawn.
 * There's the poor Lavinia Whatley in The Dunwich Horror, who goes over her head under the coaxing of her grandfather, and meets a grisly ending later one because she's not happy with the idea of destroying humanity. Most of the time women aren't so much evil as completely absent from Lovecraft's stories, since he had no idea how to write female characters.
 * As in the space of a story (days, maybe weeks) the male heroes spend time among creatures like Innsmouth hybrids or man-eating degenerate beings from The Lurking Fear, it would be pretty horrible to imagine what they could do if they weren't chaste.
 * Non Indicative Name: Cthulhu only appears in one of the original Lovecraft stories. Though he is the most iconic character in the Mythos, not all of the stories involve him--technically, "The Great Old Ones Mythos" would be a more accurate title.
 * Not So Safe Harbor: Not surprising considering how it's mostly set on New England, but Innsmouth is especially noteworthy. Also not surprising considering Lovecraft's phobia towards all things aquatic, thus marine and octopoid creatures as a consistent source of horror.
 * Occult Detective: Several characters attempt this, but often it doesn't end well. Titus Crow is a traditional example, while Teddy London is a private detective that got case involving the Mythos.
 * Our Vampires Are Different: The fungoid creature in "The Shunned House" is Lovecraft's version of a vampire. It bears little resemblance to the undead humans of other works. Other authors added "Star Vampires" and "Fire Vampires", which are even less conventionally vampire-like.
 * Paranormal Investigation
 * Plant Aliens: Both the Mi-Go and the Elder Things are described as being fungoid.
 * Poke in The Third Eye
 * Public Domain Character: Even when it was created. H.P. Lovecraft encouraged creative diversity in the original Cthulhu Circle, such that there was (and is) no single all-enjoining Canon, but rather what amounts to multiple authors' Ascended Fanon. In this sense, the Cthulhu Mythos more resembles an organic Mythology with numerous variations.
 * Psychological Horror
 * Puny Earthlings
 * Purple Prose: Lovecraft, Howard, and Smith used this often. Latter writers, not so much.
 * Retcon:
 * All over the place. Range from Derleth's ideas of morality or Smith's Greek pantheon-style genealogy (including such gems as Cthulhu being Hastur's half-brother), to Fan Wank trying to avert Science Marches On, like explaining various winged creatures like the Byakhee & Elder Things flying through space, originally ascribed to "ether", as biotechnological solar sails.
 * Lovecraft even did it to himself, such as placing the locales of some of his earlier short stories into the setting of the Dreamlands (you'll notice that 'The Cats of Ulthar', for instance, never mention being anywhere but in the real world, let alone a shared dream consciousness).
 * Sapient Cetaceans: One story in Tales from Innsmouth has the Dolphins as allies of the Deep Ones.
 * Science Fiction: Several of the various monsters are given scientific (or quasi-scientific) explanations and origins.
 * Scrapbook Story: Most famously, the original Call of Cthulhu story does this, and other writers have followed suit.
 * Shout Out: To Lovecraft and the other writers in Lovecraft's circle. What started as in-jokes became hard continuity with Adaptation Expansion.
 * References to the Mythos is also common in popular culture.
 * Sliding Scale of Idealism Versus Cynicism: Most of the time, so cynical you could use the scale as a trebuchet, competes with Warhammer 40k for the title of most Cynical popular body of fiction.
 * Spared By the Adaptation: in the 2005 silent film adaptation of The Call of Cthulhu.
 * Spell My Name With an S: Intentionally; most of the Great Old Ones and the like have names that can't be rendered in human languages, so they're spelled in all sort of different ways in different stories.
 * Starfish Aliens: All of HPL's aliens, and quite a few earth-dwelling creatures. Howard, for such an early writer, was good at ensuring his aliens were actually alien. And in the case of the Elder Things, one of the more sympathetic species, almost literal Starfish Aliens. Latter authors have followed suit.
 * Stuck in Their Shadow: In-universe example: The protagonist of Black Man With A Horn feels that his literary career was overshadowed by his friend, H.P. Lovecraft.
 * Sufficiently Advanced Aliens:
 * The Great Old Ones are some of the, er, oldest examples. All too often this aspect of them gets forgotten in favor of The Theme Park Version's literal gods.
 * In an inversion, in their introductory story, the Elder Things are presented as being men- that is, in comparison to the other aliens and horrors out there, the Elder Things built things, created a civilization, wrote, created, learned, taught. They built things and invented things. They're human compared to the nigh-godly Cthulhu Spawn and the horrific Shoggoth(s?).
 * The Taming of the Grue: You can buy Cthulhu plushie dolls. AWWWWWWWWWWWWWWWWWWWWWWWWWWWW
 * Tabletop Games: Several, including the Call of Cthulhu RPG, Trail of Cthulhu (using the GUMSHOE system and focused in the 1930's), Arkham Horror and Yellow Dawn - The Age of Hastur RPG (set in a post-apocalyptic world).
 * In addition, there was also the Mythos CCG, the Call of Cthulhu Living Card Game, and even Munchkin Cthulhu.
 * Terraform: More like de-terraform. Allies of the Mythos are trying to work towards "clearing off the Earth" for the Great Old Ones.
 * These Are Things Man Was Not Meant to Know
 * Too Many Mouths: One of the classic eldritch abomination traits. In a particularly corporeal case, the Great Old One Y'golonac (you fool, you've doomed us all!) has them on his palms.
 * Tomato in The Mirror: Several stories involve the protagonist discovering something unpleasant about his heritage.
 * Tome of Eldritch Lore: Most notably the Necronomicon, but also De Vermis Mysteriis, the Pnakotic Manuscripts, the... well just look at the list. Name-dropping one of these is a stock horror Shout Out.
 * Town With a Dark Secret: Oh so many, from Innsmouth to Jerusalem's Lot to Temphill...
 * Tuckerization: In addition to all the Author Avatars and Shout Outs, the Lovecraft Circle tossed out references to their pals:
 * Lovecraft mentions the Atlantean priest Klarkash-ton.
 * Robert Bloch wrote of the Egyptian Luveh-Keraph, priest of Bast.
 * A Comte d'Erlette wrote the Cultes des Goules.
 * Trope Overdosed: Think this page has a lot of tropes? Check out the character page.
 * Ultraterrestrials: Deep Ones, Ghouls, and Sand Dwellers.
 * Universe Concordance: Daniel Harms' The Cthulhu Mythos Encyclopedia and earlier Encyclopedia Cthulhiana.
 * The Unpronounceable:
 * All the Great Old Ones qualify.
 * In one short story a fan of Lovecraft in a world where the stories are in truth based on reality has surgery to allow her to pronounce R'lyehian correctly. This gives her an eldritch look, and when she actually practises the ability, it sort of causes the end of the world as a side effect.
 * Weaksauce Weakness:
 * The Cthonians dissolve in water. Justified: Considering the Cthonians are able to survive intense heat and pressures, can borrow underground, and have telepathic powers capable of controlling people's minds, the fact that Earth is mostly water may be the only reason why they haven't wiped humanity out.

Not a particularly exploitable weakness for the bigger ones though. Shudde-M'ell (the chief Chthonian) is described as a mile long, so immersing him in water would be ... pretty challenging.
 * Water isn't good for the Great Old Ones according to The Call of Cthulhu, either - it blocks their telepathic powers completely, trapping them to their lairs both physically and mentally, until R'lyeh rises again.
 * The Haunter in the Dark, one of Nyarlathotep's many forms, is extremely weak against light. Granted, it comes from a dimension where no visible light exists (and where it would presumably be invincible), and it can't be killed, only banished back to that dimension, but still, it's an Eldritch Abomination that can kept at bay with a flashlight! But you'd better hope your batteries last until you find something else... the Haunter can wait, it only needs to catch you once.
 * In Robert Bloch's story "The Shadow From the Steeple" (considered out of canon by some) it gets better: after a serious blunder by a university professor attempting to contain it,
 * Call of Cthulhu itself offers one. You may be surprized that, despite being an ancient and unspeakably powerful entity able to drive to insanity with nary a glance, Cthulhu is just as vulnerable as anything else to being rammed with large objects.
 * Weird Tales: Many of Lovecraft and pals wrote for the magazine.
 * When the Planets Align: The Great Old Ones will return when The Stars Are Right.
 * Who You Gonna Call: Professor Shrewsbury, Inspector Legrasse, Titus Crow, The Wilmarth Foundation, Delta Green, and Teddy London.
 * Wolverine Publicity: Cthulhu only appears in one story, yet his name is used for the whole body of fiction.
 * He only appears in one, but he's mentioned, by his name or by events from The Call of Cthulhu in many others,
 * Maybe all those references to him and pop-cultural awareness are because of his dreams reaching and influencing us?
 * Word of Dante: Several common aspects of the Cthulhu Mythos (such as the good/evil dichotomy and the Necronomicon as a powerful Brown Note) come from Lovecraft's friend, August Derleth, rather than Lovecraft himself.

''Cthulhu fhtagn... what a wonderful phrase...''