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->"That is not dead which can eternal lie,
->And with strange aeons even death may die."
-->-- Passage from the al-Azif, a.k.a. the Necronomicon,
--->from ''Literature/TheCallOfCthulhu'' by '''Creator/HPLovecraft'''

An informal and appropriately chaotic SharedUniverse that squarely defines the [[DarkerAndEdgier darkest and edgiest]] of genres, [[CosmicHorrorStory cosmic horror]].

It was started unintentionally by Creator/HPLovecraft and his circle of peers (informally called the 'Kalem Club') who belonged to the embryonic {{Fandom}}. At that stage less about SpeculativeFiction, and more about writing short amateur "weird" stories for the 'pulp' magazines, at least for Lovecraft.

Lovecraft had already incorporated small elements of Creator/RobertWChambers' earlier ''TheKingInYellow'' and the writings of Creator/ArthurMachen by way of [[ShoutOut Shout Outs]]. As time went on, Lovecraft and his friends began referring to his {{Eldritch Abomination}}s and TomesOfEldritchLore 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 AugustDerleth. Lovecraft himself called his budding mythology "Yog-Sothothery", because Yog-Sothoth features or is mentioned in many more stories than Cthulhu.

Due to the SharedUniverse's informal nature, several rather divisive conceptions of the Mythos have arisen, generally categorized as the Lovecraft purists' version; the version including the broad post-1930s expansions by later writers like AugustDerleth (who is a controversy unto himself) and Ramsey Campbell; and then there's the rigidly codified and de-mystified TabletopRPG adaptations which crunch down MindScrewdriver-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 [[AdaptationDisplacement majority of pages]] derived from the game and its various campaigns, rather than from prose literature (let alone Lovecraft's writings), which are not always labeled as such.

Creator/HPLovecraft 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 CosmicHorrorStory (for works which deal with Lovecraft's ''themes'' (and, optionally, make use of the Mythos) and LovecraftLite for works that take Lovecraft and Mythos less seriously.

See also the [[TabletopGame/CallofCthulhu Call of Cthulhu RPG]].


[[folder: Related Settings]]
!!Sub-settings within the Cthulhu Mythos 'verse include:
* Lovecraft's own inventions of '''Arkham''' (containing '''Miskatonic University'''), '''Dunwich''', '''Innsmouth''', and '''Kingsport''', TropeNamer for LovecraftCountry.
* '''The Dreamlands''': Also created by Lovecraft and inspired by the work of Creator/LordDunsany. A fantastical world created by people's dreams, more subtly horrific.
* '''Hyperborea''': Prehistoric Greenland prior to the Ice Age. Created by Creator/ClarkAshtonSmith, it focuses more on weirdness than CosmicHorror. Smith's '''Zothique''' stories, set on Earth's last continent, have a similar emphasis.
* '''Literature/{{Kull}}''', '''Franchise/ConanTheBarbarian''', and '''Literature/BranMakMorn''': Creator/RobertEHoward's works form a peripheral part of the Mythos. The stories tend to be human-centric. "Literature/TheTowerOfTheElephant", one of the best early Conan stories, features a Lovecraftian abomination and subverts the mythos by making it sympathetic.
* '''TabletopGame/DeltaGreen''': The Mythos meets government conspiracies and black ops. It began as a supplement for the ''Call of Cthulhu'' RPG game.
!![[http://en.wikipedia.org/wiki/Category:Cthulhu_Mythos_writers Notable Cthulhu Mythos writers include]]:
[[folder: The "Lovecraft Circle"]]
!! The original writers who corresponded with each other and used the elements of the mythos in their writings.
* Creator/HPLovecraft: [[CaptainObvious Obviously.]] His works (referred as the "Yog-Sothoth Cycle" or the "Lovecraft Mythos") form the central nucleus of the milieu.
* AugustDerleth: Co-founder of Arkham House, and codifier of the Mythos. Also see ''Literature/TheTrailOfCthulhu''.
* Creator/ClarkAshtonSmith.
* DonaldWandrei: Co-founder of Arkham House.
* Creator/HenryKuttner.
* FrankBelknapLong.
* Creator/RobertBloch.
* Creator/RobertEHoward.

[[folder: Pre-Lovecraft Authors]]
!! Writers whose works were before Lovecraft started, but were a great influence on him. Later {{retcon}}ned into the Mythos:
* Creator/AmbroseBierce: Created the lost city of Carcosa and the name Hastur, which reappear in ''Literature/TheKingInYellow''.
* Creator/LordDunsany: Inspired Lovecraft's dream-prose period and the idea of creating a pantheon of his own.
* RobertWChambers: Wrote ''TheKingInYellow'', which was a great inspiration for Lovecraft, and was, in turn, inspired by Bierce.
* Creator/ArthurMachen: Wrote ''Literature/TheGreatGodPan'', inspiring Lovecraft's take on {{Half Human Hybrid}}s, especially in "The Dunwich Horror".

[[folder: Post-Lovecraft Writers]]
!! Notable authors who have written in the mythos after Lovecraft had passed away:
* Creator/FritzLeiber. Technically a contemporary, but published wrote stories set in the continuity only later.
* Creator/BrianLumley: A prolific writer whose TitusCrow, ''Primal Land'', and ''Hero of Dreams'' works forms a part of the mythos.
* Creator/ChiakiKonaka: Who has written several Mythos stories in addition to his work as an anime screenplay writer.
* LinCarter: The major scholar and archivist of the Mythos, as well an editor and writer.
* RamseyCampbell: Notable for founding CampbellCountry.
* C. J. Henderson: Known for combining mystery with the Mythos. Some focus on Inspector Legrasse and others private eye Teddy London.
* Creator/StephenKing: Contributed a couple of stories set in the Mythos.
* Creator/ThomasLigotti: 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."
* Creator/GrahamMasterton: draws on the Cthulu mythos, or at least some of its original referents on Native american mythology, for works such as ''Literature/TheManitou'' and the ''Night Warriors'' series.
* Creator/WHPugmire: Writes Mythos stories set in Sesqua Valley, his own creation.
* Creator/CharlesStross: Has written ''TheLaundrySeries'', about government agencies focused on the occult, as well as several short standalone stories of the Cosmic Horror variety.
!!'''The Mythos includes such specimens as''':


[[folder: Tropes A-F]]
* AbsoluteXenophobe: Yekubians, a alien species who destroyed all other intelligent life in their home galaxy.
* AffectionateParody: See LovecraftLite. A canon example with Derleth's "The Whippoorwills in the Hills", which is a quasi-sequel to "The Dunwich Horror". As if to follow up the parody at the end of "Horror", Derleth parodies the ending of another of Lovecraft's work.
* AlienAnimals: Cats, at least in the Dreamlands, are intelligent, speak their own languages, and can leap across space. They're also at war with the Cats from Saturn.
* AlienGeometries: One of the most notable examples being on the island of R'lyeh, in "The Call of Cthulhu".
* AliensAreBastards: Just about everything not of this Earth is evil and/or horrifying. About the only exception are Elder Things 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. Nodens is probably the most pleasant, earthly-seeming deity, and even he only helps unfortunate humans on a whim.
* AlienSky:
** The World of Seven Suns, orbited by seven stars.
** Shaggai orbits twin green stars. Xoth (Cthulhu's original homeworld) is also said to orbit twin green suns.
* AllMythsAreTrue: Some characters theorize that all human mythologies are inspired by the Mythos in one way or another. Even the concepts of good versus evil is influenced by the conflict between the Elder Gods and the Great Old Ones (despite both being [[BlueAndOrangeMorality beyond good and evil]]).
* AlternateContinuity:
** Many of the parodies tend to use the mythos, but have their own spin on them.
** One example is ''[[TheLaundrySeries The Laundry Series]]'' by Creator/CharlesStross. Set in the present day, mostly in the UK, in a top-secret, high-tech government agency devoted to staving off "when the stars are right" for as long as possible. TabletopGame/DeltaGreen [[XMeetsY meets]] ''[[Series/TheOfficeUK The Office]]'' meets [[SpyFiction Stale Beer Spy Fiction]]. The monsters are real, the aliens and Deep Ones share the Earth with us... and most governments have secret Occult Intelligence divisions.
* AlwaysChaoticEvil: The majority of beings in the Mythos - the Deep Ones, Great Old Ones, the Tcho-tcho, the Insects from Shaggai - come off as this. Sometimes may be due to how [[BlueAndOrangeMorality alien]] these beings are. Sometimes not.
* AncientAstronauts: In addition to Lovecraft's Cthulhu, Elder Things, Mi-go, Yithians, and Flying Polyps, later writers added the Shan, Star Vampires and Yuggs.
* AnotherDimension: Where Cthulhu and the Mi-go originated. Also the Dreamlands.
* APlanetNamedZok: Most every planet mentioned in the Mythos follows this, the most well-known being Yuggoth.
* ApocalypseCult: Most (if not all) of the Mythos cults are trying to bring back the Great Old Ones, which would end up destroying the world.
* ApocalypticLog: Often found by investigators, and some stories are entirely these.
* ArtisticLicenseGeology: Islands or whole continents rising out of seas. This was the result of Lovecraft and pals cribbing from the Theosophists (using their ideas about Atlantis and Lemura to lend a sense of authenticity), as well as [[ScienceMarchesOn the science of the time]]. Latter writers knew the scientific impossibility, but [[RuleOfCool just ran with it for the sake of coolness]].
* ArtifactOfDoom: Plenty, but the [[AlienGeometries Shining Trapezohedron]] is probably the most noted. Also an ArtifactOfDeath, if you differentiate between the two.
* AssholeVictim: A common occurrence. Though, the reader may feel pity towards these characters because of their ''horrific fates''.
* AuthorAppeal: Being a lover of cats, Lovecraft tended to treat felines rather fondly in his works. Friends and later writers would actually add Lovecraft into his own Mythos because of his influence.
* AuthorAvatar:
** 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.
** Creator/RobertBloch 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".
** Later, Bloch wrote a sequel which mentions both the [[{{Expy}} Expies]] ''and'' 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 Creator/ClarkAshtonSmith.
** "HPL" by Creator/GahanWilson even has Lovecraft (and Clark Ashton Smith) as summoners of [[EldritchAbomination 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.
* BasedOnAGreatBigLie: A good many of the tales are supposed to be documents, diaries, or excerpts from elder lore. In-universe, some are even referenced as some newspaper story "purported to be truth" but are met with skepticism.
* BenevolentConspiracy: Most of the anti-Mythos groups operate covertly. The Wilmarth Foundation do this to prevent panic and hide from the minions of the Great Old Ones. While very ruthless, TabletopGame/DeltaGreen conspires to save America from unspeakable horror.
* BizarreAlienBiology: 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".
* BlackSpeech: R'lyehian, the language used by Cthulhu and his spawn. Eventually, it was passed down from aeons to be used by the minions of the Mythos. It's also used in general to summon various Great Old Ones or their minions, even those not directly linked to Cthulhu.
--> '' ph'nglui mglw'nafh Cthulhu R'lyeh wgah'nagl fhtagn''
* BlueAndOrangeMorality: 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".
* CanonWelding: Very common.
* ChaosIsEvil: Nyarlathotep, the "Crawling Chaos", is a sinister figure. The Lurking Chaos, Xexanoth, is considered blasphemous. Literally with Azathoth.
* ChristmasEpisode: Lovecraft's "The Festival".
* CityWithNoName: "The Nameless City".
* ContinuityNod: Given they are part of a SharedUniverse, this is inevitable with many stories in varying degrees, ranging from very subtle such as an off-hand reference to Miskatonic University or the Necronomicon to more obvious ones like incorporating famous abominations, to outright referencing plot points from Lovecraft's stories, all of which can be put to great use depending on the nature of the tale.
* ContinuityPorn: Common from virtually the moment of Lovecraft's death onwards, though hardly mandatory.
** If you consider many of the stories are narrated in first person and one of the bases of the Mythos is that humans actually know really little about the cosmos then we can conclude that the narrators don't know enough or have wrong information due to the vague nature of their sources about the Mythos, which of course is a nice excuse to keep creating new stuff.
* CoversAlwaysLie: Lovecraft anthologies (especially ones by Del Rey) often have weird, surreal imagery unrelated to anything in the stories. Though they do communicate the atmosphere of the books well enough.
* CreepyCemetery: "The Walker in the Cemetery" by Ian Watson is set in one of these.
* CrypticBackgroundReference: Lovecraft did this often, and so did the Kalem Club, throwing out little bits and pieces of elder lore. It left fans wondering and wanting for more. Trying to piece them all together is part of the stories' appeal.
* {{Cult}}s: The Mythos is filled with Old One worshipers with [[ReligionOfEvil 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.
* CulturalCrossReference: Mythos references have been made in Japan ranging from the subtle (''Anime/TheBigO'', ''Franchise/{{Digimon}}'') to the blatant (''LightNovel/HaiyoreNyarkoSan'').
* DarkFantasy: Really Dark.
* DeathByAdaptation: [[spoiler:Inspector Legrasse]] in the 2005 silent film adaptation of ''[[LovecraftOnFilm The Call of Cthulhu]]''. [[spoiler:In the story, he not only lives, but some writers used in their own short stories.]]
** The same goes for a bunch of other characters in ''[[LovecraftOnFilm The Whisperer In Darkness]]'' as well. Most prominently, [[spoiler: Albert Wilmarth crashes a plane into a Mi-Go ritual site, after which the aliens [[BrainInAJar save his brain]]]].
* DidYouJustRomanceCthulhu:
** Lovecraft's "The Dunwich Horror". Yog-Sothoth mates with a human woman and produces the offspring who will be known as Wilbur Whateley.
** Michael Shea's "Fat Face". An "escort" seeks comfort from a large, seemingly kindly man. [[spoiler: It's not a man, and it doesn't end well.]]
** Played with Ramsey Campbell's "The Faces At Pine Dunes". The protagonist and his girlfriend investigate his parents' strange behavior. [[spoiler: His father is a Human[=/=]EldritchAbomination hybrid, and so is the protagonist.]]
* DivineRanks: The Mythos developed a hierarchy of entities, but it wasn't formalized until later.
* TheDreaded: 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 TropeCodifier of EldritchAbomination for a reason.
* DugTooDeep: Happens in a Lumley tale [[spoiler:in which an oil drill ends up drilling into a sleeping Great Old One.]]
* EarthIsTheCenterOfTheUniverse: Played with - the primary reason that so many sealed evils are concentrated on Earth is precisely because they are ''not'' concentrated on Earth. There's just so damned many of them that Earth ends up having its fair share of octopoid elder gods as a matter of normal statistical distribution.
** In ''TheDunwichHorror'', young Whateley's diary states that the alien intelligences are interested in Earth as an element in their long-range plans. Organic life, on the other hand, is considered an obstruction, and their real plans can get started once they erase all life on Earth and take it out of three-dimensional space.
* EldritchAbomination: For all practical purposes, this is the [[TropeMaker font and origin of all blobby god-things with unpronounceable names]].
* EldritchLocation: Lots and lots.
* ElementalEmbodiment: August Derleth had used an Elemental Theory: the idea that the Old Ones can be sorted by the four classical elements; for example, Cthulhu for water, and Derleth creations Cthugha and Ithaqua for fire and air, respectively.
* EvilDetectingDog: In ''TheColourOutOfSpace", cats end up leaving the accursed farm, likely knowing what really landed.
* EvilOnlyHasToWinOnce: If any of the Great Old Ones are ever freed or awakened fully, then it's good-bye to mankind.
* EvilSmellsBad:
** In general the Great Old Ones smell "foul", a sign people would know them. In Cthulhu's case, he probably wouldn't smell so good after being stuck in a tomb for millions of years.
** Ill-reputed Innsmouth smells like fish.
* ExpandedUniverse: A rather informal one, with Lovecraft's tales being the nucleus of the chaos.
* ExternalRetcon: Happens, but most notable with Hastur.
* EyesDoNotBelongThere: Wilbur Whateley has eyes where they should not be.
* FantasyKitchenSink: Despite not being a real mythology, the Mythos tends to get tossed into such stories.
* FantasyPantheon: With three sets of them!
* FictionalDocument: The various unspeakable books, commentaries on said books, as well as the various final testaments.
* FishPeople: The Deep Ones and their HalfHumanHybrids, obviously.
* FusionFic: Such fan fics are rather common.

[[folder: Tropes G-L]]
* GenocideBackfire: ''The Doom that Came to Sarnath''.
* GoMadFromTheRevelation: TropeNamer.
* GratuitousGerman: The ''Unausprechlichen Kulten''. According to S T Joshi, a leading Lovecraft authority and who provides the annotations for Lovecraft's stories for the Penguin Classics editions, it's also ''wrong'' German. It should be "Die Unausprechlich Kulten". Odd, since Lovecraft spoke German. And it's still wrong: The correct form would be either "Unaussprechliche Kulte", "Die unaussprechlichen Kulte" or "Von Unaussprechlichen Kulten" (note the capitalization).
* TheGreatestStoryNeverTold: People journey into the depths of horror, sometimes preventing such nightmares from rising - and very few (if anyone) actually learn of the tale.
* HalfHumanHybrid: And not the [[BodyHorror cute furry kind]], [[InTheBlood nor the sympathetic outcast kind]].
* HeKnowsTooMuch: Whoever finds out too much about the Mythos (such as the Cthulhu Cult) [[KilledToUpholdTheMasquerade tends to be hunted down and killed]]. That is, if the person in question doesn't go insane first or get eaten.
* HistoricalDomainCharacter: 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. ''Webcomic/LovecraftIsMissing'' is a prominent example.
* HomeworldEvacuation: The Insects From Shaggai (AKA Shan) in Ramsey Campbell's stories. When their home planet was destroyed by a Mythos abomination, some of them fled to a succession of other planets, finally ending up on Earth.
** Yith itself is a ''dead'' planet, but the Great Race which evolved there fled to primordial Earth via mass mind-swap.
* HostileTerraforming: Allies of the Mythos are trying to work towards "clearing off the Earth" for the Great Old Ones.
* HowWeGotHere: Typically of the "See, this is why I must commit suicide before sundown..." variety.
* HumanSacrifice: Whether it's being used in some unspeakable experiment/ritual or just being a snack for an Old One, it's very common.
* HumansAreCthulhu: As shocking as it may seem there are some stories, even by Lovecraft himself, where humans are not at the bottom of the cosmic food chain. For instance "Memory" has a daemon and a genie talking about a race that built the ancient ruins in a valley: [[spoiler: Man]]. And in "Through the Gates of the Silver Key" Randolph Carter possesses an alien from the distant past who is "disgusted by the thought of the human earth-mammal" [[spoiler: that holds him prisoner in his own body for millions of years, long after the rest of his race is extinct.]]
* IHaveManyNames: 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 TheScottishTrope where the true name is forbidden (even "Azathoth" is a pseudonym).
* InsectoidAliens: The Mi-Go and the Insects From Shaggai.
* {{Kaiju}}: There are some ''really'' big monsters in the Mythos. Cthulhu is described as a walking "mountain". Most of his children are almost as large- one of them whose ''talons alone'' are the size of mountains. Not to mention Dagon, Zhar and Lligor, several of Nyarlathotep's masks... all big. And then there's Ghroth, a monster the size of a ''planet''.
* LivingBodysuit: Nyarlathotep, Hastur, Y'Golonac, and the Insects from Shaggai.
* LizardFolk: The Serpent Men of Howard's Conan stories, and later used by Lovecraft.
* LoadsAndLoadsOfRaces: HPL himself mentioned or sometimes showed a [[http://en.wikipedia.org/wiki/Elements_of_the_Cthulhu_Mythos#Beings few dozen aliens and monsters]], and subsequent authors and co-writers have expanded this greatly. That's not even getting into the godlike deity-aliens. Overall there are at least 30 intelligent races described.
* LockedOutOfTheLoop: Upper-class Anglo-Saxons seem to be the only people on Earth unaware of the horrors going on.
* LovecraftLite
** The stories by Smith, Derleth, Lumley, and Howard, in particular. Smith's tales focus on the weirdness rather than the horror, 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.

[[folder: Tropes M-R]]
* MagicFromTechnology: Often hinted that the "magic" of the Mythos is just advanced science.
* MagicIsEvil: There are plenty of evil (and insane) sorcerers. However, there are also examples of good people using "magic" to stop the bad guys. TitusCrow is one example, and Lovecraft's [[TheDunwichHorror Professor Armitage]] is another. It's hinted that the magic may not be evil outright, [[GoMadFromTheRevelation just extremely dangerous to us ignorant humans]]. It's this interpretation that the ''TabletopGame/CallOfCthulhu'' RPG takes, where using spells will sap Sanity.
* {{Masquerade}}: One of the defining aspects of the Mythos, living in ignorance of the true horrors of reality.
* MediumAwareness: 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 MoralGuardian 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.
* MistakenForQuake: When the ground shakes in a Mythos tale, you can bet it's either a Cthonian hive nearby or something ''worse''.
* MoeAnthropomorphism: You can find most, if not all, of the mythos beings depicted as human girls. Cthylla is notable here since, being called Cthulhu's daughter, it's much easier to search for her moe art than her squid-like form. LightNovel/HaiyoreNyarkoSan takes this to [[UpToEleven the next level]], with Nyarlathotep, Cthugha, and Atlach-Nacha as cute {{moe}} girls.
* MoreThanThreeDimensions: This trope is all over the Mythos. Most of its famous monstrosities exist in many more dimensions than we humans can perceive, so what we do see are just limited projections of their true multidimensional forms onto the 3D "reality".
* MultipleChoicePast: Details vary between story to story, even if it's the same author. It may have been done on purpose to create a sense of ambiguity.
* MushroomMan: The Fungi from Yuggoth.
* MysteriousAntarctica: "Literature/AtTheMountainsOfMadness", as well as the material that follows up on the plot, such as roleplaying supplements and the novel ''Hive''.
* NamesToRunAwayFromReallyFast: Pretty much all of them, unsurprisingly.
* NoBiologicalSex: Almost all the monsters created by Lovecraft himself are sexless. The only exceptions are the Deep Ones.
* NoHuggingNoKissing:
** Lovecraft's stories contain virtually no hanky-panky. His narrators are universally chaste. Female characters are almost 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. The only even semi-notable exception is the unnamed mother of Charles Dexter Ward, who, while remaining a side character, deeply loves her son and falls ill out of concern for him; when her husband discovers what their son is really up to, he does everything he can to keep her from knowing just how awful things really are out of fear that he'd lose her forever, either mentally or altogether, from the shock.
** There's the poor Lavinia Whateley in ''Literature/TheDunwichHorror'', [[spoiler: who goes over her head under the coaxing of her grandfather, and meets a grisly ending later on 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. [[spoiler:Even Asenath Waite was actually the spirit of a man inhabiting the body of his daughter.]]
** As in the space of a story (days, maybe weeks) the male heroes spend time among creatures like [[HalfHumanHybrid Innsmouth hybrids]] or [[IAmAHumanitarian man-eating degenerate beings]] from ''The Lurking Fear'', it would be pretty horrible to imagine what they could do if they ''weren't'' chaste.
** Averted with Smith and Campbell, where romance plays a role in some of their stories.
* NonIndicativeName: Cthulhu only appears in one of the original Lovecraft stories, and his role beyond that one is fairly minimal. Though he is the most iconic character in the Mythos, he is definitely not the central figure--technically, "The Great Old Ones Mythos" would be a more accurate title.
* NotSoSafeHarbor: Not surprising considering how it's mostly set on NewEngland, 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.
* OccultDetective: Several characters attempt this, but often it doesn't end well. TitusCrow is a traditional example, while Teddy London is a private detective that worked on cases involving the Mythos.
* TheOldGods: The Great Old Ones and the Outer Gods. Averted with the Elder Gods, who imprisoned the Great Old Ones.
* OurTitansAreDifferent: The Great Old Ones once ruled the cosmos, but are now trapped, limited in power, or sleeping.
* OurVampiresAreDifferent: 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.
* ParanormalInvestigation: Plenty of investigators, and very few survivors.
* PerspectiveFlip:
** "The Litany of Earth" tells the story of one of the survivors of Innsmouth, thematically engaging with Lovecraft's fear of the other.
** The works of Creator/WHPugmire do this a lot. Most of his protagonists are non-human and linked to Lovecraftian entities.
* PickyPeopleEater: Some of the horrors of the mythos want blood or brains instead of eating people entirely.
* PlantAliens: Both the Mi-Go and the Elder Things are described as being fungoid.
* PokeInTheThirdEye: In Long's ''The Hounds of Tindalos'', the protagonist, using mental time travel ends up going too far back in time, and attracting some really unwanted attention.
* PopCulturalOsmosis: Thanks to the innumerable pop culture references, people have learned about the Mythos from almost everything but the original stories.
* PosthumousCollaboration: Several stories were finished after Lovecraft's death by Derleth.
* ProductPlacement: Partly a ShoutOut - in one of Derleth's stories, the characters acquire the anthology "The Outsider and Others" by H.P. Lovecraft for their investigation. "The Outsider" was the first book published by ''Arkham House'', Derleth's and Donald Wandrei's company that was founded to help preserve Lovecraft's legacy. It was also a practical way to get the word out to the fans.
* PublicDomainCharacter: 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' AscendedFanon. In this sense, the Cthulhu Mythos more resembles an organic {{Mythology}} with numerous variations.
* PsychologicalHorror
* PunyEarthlings: Everyone else in the cosmos is either vastly stronger, powerful, or more advanced than the fragile-minded humans.
* PurpleProse: Lovecraft, Howard, and Smith indulged in this. Later 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 FanWank trying to avert ScienceMarchesOn, 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.)

[[folder: Tropes S-Z]]
* SapientCetaceans: A story in ''Tales from Innsmouth'' has dolphins as allies of the Deep Ones.
* SatanicArchetype: Nyarlathotep is more or less Satan, if not worse. A shape changer, sometimes humanoid (as the Black Pharaoh in "Nyarlathotep"), sometimes a hideous EldritchAbomination (as The Haunter of the Dark in the story of the same name); diabolical pact-maker (to Keziah Mason in "The Dreams in the Witch House"), trickster (to [[spoiler: Randolph Carter]] in "The Dream-Quest of Unknown Kadath"). Although he does act as TheDragon for [[MadGod Azathoth]], Nyarlathotep can be seen as a physical manifestation of the Outer Gods' will (Yog-Sothoth and Azathoth), and is referred to as their 'soul and messenger' more than once, which means the Outer Gods are colossal bastards. He's also the only one of them with a human mindset, and has active interest in humanity. This isn't a good thing. AT ALL.
** Specifically, ''most'' of the entities these stories revolve around are basically uninterested in humans as a matter of scale: They exist at least as far above us in the scale of the cosmos as we do above ants. Humanity's primary defense against them is ''being completely beneath notice''. Nyarlathotep, however, has plans for which humans happen to be ''ideal''.
* ScienceFiction: Several of the various monsters are given scientific (or quasi-scientific) explanations and origins.
* ScrapbookStory: Most famously, the original ''Call of Cthulhu'' story does this, and other writers have followed suit.
* SentientCosmicForce: Yog-Sothoth for the Space-Time Continuum. The various Outer Gods could be interpreted to be this. For example, every nuclear reaction is Azathoth.
** At least one version says Azathoth's physical presence ''was the big bang''.
* SeriesMascot: Cthulhu, naturally; it's neither the most powerful of the Outer Gods nor their leader, but it's the most famous because of the story it was featured in.
* ShoutOut: To Lovecraft and the other writers in Lovecraft's circle. What started as in-jokes [[RunningTheAsylum became hard continuity]] with AdaptationExpansion. References to the Mythos are also common in popular culture.
* SlidingScaleOfIdealismVersusCynicism: 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.
* SortingAlgorithmOfEvil: In essence, there are three tiers to the Mythos; at the bottom are the "mere" horrors -- aliens, ghouls, mad sorcerers, etc. Above these are the Great Old Ones, which are basically {{Physical God}}s. And above ''these'' are the Outer Gods, which are to the Great Old Ones what the Great Old Ones are to the lesser races. To put it in perspective, ''Cthulhu'' '''worships''' the Outer Gods.
* SpacetimeEater: Conversed between the narrator and a Lovecraft-expy in Long's "The Space Eaters". They talk about Eldritch Abominations in general, with the Expy asking what would happen if they "eat their way to us through space!"
* SparedByTheAdaptation: [[spoiler:The narrator]] in the 2005 silent film adaptation of ''[[LovecraftOnFilm The Call of Cthulhu]]''. [[spoiler: The beginning of the original story refers to the "late" Francis Wayland Thurston. How he died is not revealed. The movie doesn't really hint at this at all.]]
* SpellMyNameWithAnS: Intentionally; most of the Great Old Ones and the like have names that [[TheUnpronounceable can't be rendered in human languages]], so they're spelled in all sort of different ways in different stories.
* SpotlightStealingTitle: Despite being the most well known and iconic character, Cthulhu himself has only a few small appearances in the stories and is more of a minor background character compared to Yog-Sothoth, Dagon, and Nyarlathotep.
* StarfishAliens: 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 [[http://en.wikipedia.org/wiki/Elder_Things Elder Things,]] one of the more sympathetic species, almost ''literal'' StarfishAliens. Later authors have followed suit.
* StuckInTheirShadow: In-universe example: The protagonist of ''Black Man With A Horn'' by T.E.D. Klein feels that his literary career was overshadowed by his friend H.P. Lovecraft.
* {{Sufficiently Advanced Alien}}s:
** The Great Old Ones are some of the, er, oldest examples. All too often this aspect gets ignored in favor of TheThemeParkVersion'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?).
* SufficientlyAdvancedBambooTechnology: Many of the alien tech look like they're ancient stone ruins or tools. Some of it is actually so very advanced it may be beyond human comprehension.
* SuperweaponSurprise: Of the Bigger Brother variety, in Lovecraft's Dreamlands stories "The Doom that Came to Sarnath" and "The Other Gods", to name a few. (Not in stories set in our world, though, or else said Bigger Brothers would have wiped humanity off the page.)
* TheTamingOfTheGrue: You can buy [[EverythingsBetterWithPlushies Cthulhu plushie dolls]]. [[http://images.google.com/images?hl=en&source=imghp&biw=1280&bih=610&q=cthulhu+plush&gbv=2&aq=f&aqi=g2&aql=&oq=&gs_rfai= Adorable, aren't they]]?
* TabletopGames:
** Spawned several [=RPGs=], including the ''TabletopGame/CallOfCthulhu'' RPG, ''Trail of Cthulhu'' (using the GUMSHOE system and focused in the 1930's), ''TabletopGame/ArkhamHorror'' and ''Yellow Dawn - The Age of Hastur'' RPG (set in a post-apocalyptic world).
** The franchise also inspired Card Games, like the ''Mythos'' [[CollectibleCardGame CCG]], the ''Call of Cthulhu Living Card Game'', and even ''[[{{Munchkin}} Munchkin Cthulhu]]''.
* TheseAreThingsManWasNotMeantToKnow: The entire Mythos is filled with these.
* ThroughTheEyesOfMadness: Several stories by Lovecraft, who was likely inspired by Chambers.
* TomatoInTheMirror: Several stories involve the protagonist discovering something unpleasant about his heritage.
* TomeOfEldritchLore: Most notably the ''Necronomicon'', but also ''De Vermis Mysteriis'', the ''Pnakotic Manuscripts'', the... well just [[http://en.wikipedia.org/wiki/Cthulhu_Mythos_arcane_literature look at the list.]] Name-dropping one of these is a stock horror ShoutOut.
* TooManyMouths: One of the classic EldritchAbomination traits. In a particularly corporeal case, the Great Old One Y'golonac ([[RunningGag you fool]], [[SpeakOfTheDevil you've doomed us all!]]) has them on his palms.
* TownWithADarkSecret: Oh so many, from ''Innsmouth'' to ''Jerusalem's Lot'' to ''Temphill''...
* TropeOverdosed: Think this page has a lot of tropes? Check out the character page.
* TheTropeWithoutATitle
* {{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 ''[[Creator/ClarkAShtonSmith Klarkash-ton]]''.
** Robert Bloch wrote of the Egyptian ''[[Creator/HPLovecraft Luveh-Keraph]]'', priest of Bast.
** A ''[[AugustDerleth Comte d'Erlette]]'' wrote the ''Cultes des Goules''.
* {{Ultraterrestrials}}: Deep Ones, Ghouls, and Sand Dwellers.
* UniverseConcordance: Daniel Harms' ''The Cthulhu Mythos Encyclopedia'' and earlier ''Encyclopedia Cthulhiana''.
* TheUnpronounceable:
** 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.
* WeaksauceWeakness:
** The Cthonians ''dissolve in water.'' Justified: Considering the Cthonians are able to survive intense heat and pressures, can burrow 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 EldritchAbomination that can kept at bay with ''a flashlight''! But you'd better hope [[TenSecondFlashlight your batteries last]] until you find something else... the Haunter can wait, it only needs to catch you once.
*** In Creator/RobertBloch's story "The Shadow From the Steeple" (considered [[FanonDisContinuity out of canon by some]]) it gets better: after a ''serious'' blunder by a university professor attempting to contain it, it [[GrandTheftMe takes over his body]], therefore becoming almost unaffected by light, changes the man's field of expertise to theoretical physics, then joins the Manhattan project so we'll succeed in creating a weapon that could actually annihilate us. It's also an avatar of the god Nyarlathotep, [[NamesToRunAwayFromReallyFast The Crawling Chaos]].
** ''Call of Cthulhu'' itself offers one. You may be surprised that, despite being an ancient and unspeakably powerful entity able to drive humans to insanity with nary a glance, Cthulhu is just as vulnerable as anything else to being rammed with large objects.
* WeirdTales: Lovecraft and many of his friends wrote for the magazine.
* WhenThePlanetsAlign: The Great Old Ones will return when ''The Stars Are Right''.
* WhoYouGonnaCall: Professor Shrewsbury, Inspector Legrasse, Titus Crow, The Wilmarth Foundation, Delta Green, and Teddy London.
* WolverinePublicity: Cthulhu only appears in one story, yet his name is used for the whole body of fiction. Justified in that Cthulhu or the events from The Call of Cthulhu is alluded to in other stories.
* YouCannotGraspTheTrueForm: Contrary to popular belief, people can see the true form of many eldritch beings just fine. It's just sometimes the truth is just too much for the human mind. But there's a few that do play the trope straight. See the [[Characters/CthulhuMythos Character page]] for more detail.
''Cthulhu fhtagn... what a wonderful phrase...''