A shoggoth (occasionally shaggoth) is a monster in the Cthulhu Mythos. The being was mentioned in passing in sonnet XX ("Night-Gaunts") of H.P. Lovecraft's sonnet cycle Fungi from Yuggoth, written in 1929–30, and were expounded upon in his novella At the Mountains of Madness (1931).
|“||It was a terrible, indescribable thing vaster than any subway train—a shapeless congeries of protoplasmic bubbles, faintly self-luminous, and with myriads of temporary eyes forming and un-forming as pustules of greenish light all over the tunnel-filling front that bore down upon us, crushing the frantic penguins and slithering over the glistening floor that it and its kind had swept so evilly free of all litter.||”|
— H. P. Lovecraft, At The Mountains of Madness
The definitive description of shoggoths comes from the above-quoted story. In it, Lovecraft writes them as massive amoeba-like creatures looking like they are made out of tar, with multiple eyes "floating" on the surface. They are described as "protoplasmic", lacking any default body shape and instead being able to form limbs and organs at will. An average shoggoth measured fifteen feet across when a sphere, though the story mentions ones of much greater size.
Mythos media most commonly shows them, although intelligent to some degree, dealing with problems using their great size and strength. For instance, the original one mentioned in At the Mountains of Madness simply rolled over and crushed giant albino penguins that were in the way as it pursued the characters.
The character of the Mad Arab, Abdul Alhazred, found the mere idea of their existence on Earth terrifying.
Origin and history 
The shoggoths were created by the Elder Things. Being amorphous, they could take on any shape needed, making them very versatile within their aquatic environment. Though able to "understand" the Elder Things' language, they had no real consciousness and were controlled through hypnotic suggestion.
The shoggoths built the underwater cities of their masters. Over millions of years of existence, some shoggoths mutated and gained independent minds. Some time after this, they rebelled. Eventually, the Elder Things succeeded in quelling the insurrection, but thereafter watched them more carefully. By this point, exterminating them was not an option as the Elder Things were fully dependent on them for labor and could not replace them. It was during this time that, despite their masters' wishes, they demonstrated an ability to survive on land.
Within the Mythos, the existence of the shoggoths possibly led to the accidental creation of Ubbo-Sathla, a god-like entity supposedly responsible for the origin of all life on Earth, though At The Mountains of Madness brings up the possibility of the Elder Things being the creators, having made early life as discarded experiments in bioengineering.
Other connections 
When the Elder Things retreated to the oceans, they took the shoggoths with them, but also out of desperation let them develop the ability to exist on land. In contrast to their failing society, the shoggoths began to imitate their art and voices, taking over the cavern city underneath Antarctica and creating a twisted imitation of the society of their masters.
Aside from their main appearance in the Mountains of Madness story, shoggoths also appear in other Mythos stories, often as servitors or captives to powerful cults and entities. They are known to endlessly repeat "Tekeli-li", a cry that their old masters used.
Other appearances 
- Shoggoths are mentioned in the Lovecraft short stories "The Shadow Over Innsmouth" (1931) and "The Thing on the Doorstep" (1933).
- Shoggoths appear in both the Chaosium and the Wizards of the Coast Call of Cthulhu role-playing game supplements.
- Shoggoths are featured in Charles Stross's novelette "A Colder War", in which they are used as weapons of mass destruction. In The Atrocity Archives, the Iraqi Intelligence Service was said to be collaborating with Yusuf al-Qaradawi on raising shoggoths for use in combating the West.
- The Hive trilogy by Tim Curran features shoggoths when a modern expedition returns to the site of At the Mountains of Madness.
- Two shoggoths are present in the video game Call of Cthulhu: Prisoner of Ice as the titular prisoners.
- A shoggoth is a key boss in the multi-platform video game Call of Cthulhu: Dark Corners of the Earth.
- Shoggoths appear as major foes in the novel The Spiraling Worm by David Conyers and John Sunseri.
- Shoggoths appear alongside Cthulhu in the Scribblenauts games.
- Elizabeth Bear's novelette "Shoggoths in Bloom" explores the themes of volition and slavery suggested by the shoggoth origin.
- There is a Lovecraft-inspired Fiddler on the Roof parody-musical entitled A Shoggoth on the Roof .
- In the Japanese light novel My Maid is an Amorphous Blob (うちのメイドは不定形) by Shizukawa Tasso, the maid Tekeli is a shoggoth with human shape.
- Shoggoths and Cthulhu are mentioned in 'Illuminatus' by Robert Anton Wilson
- Burleson, Donald R. (1983). H. P. Lovecraft, A Critical Study. Westport, CT / London, England: Greenwood Press. ISBN 0-313-23255-5.
- Harms, Daniel (1998). "Shoggoths". The Encyclopedia Cthulhiana (2nd ed. ed.). Oakland, CA: Chaosium. pp. 273–4. ISBN 1-56882-119-0.
- Lovecraft, Howard P. (1985) . "At the Mountains of Madness". In S. T. Joshi (ed.). At the Mountains of Madness and Other Novels (7th corrected printing ed.). Sauk City, WI: Arkham House. ISBN 0-87054-038-6. Definitive version.
- Pearsall, Anthony B. (2005). The Lovecraft Lexicon (1st ed. ed.). Tempe, AZ: New Falcon Pub. ISBN 1-56184-129-3.
- This spelling appears in the original Arkham House printing for "The Thing on the Doorstep" (1937 or shuggoth), though the definitive manuscripts show that the proper spelling is in fact "shoggoth". (Burleson, H.P. Lovecraft, A Critical Study, footnote #14, p. 195.)
- This cry is a reference to the Edgar Allan Poe novel The Narrative of Arthur Gordon Pym of Nantucket, which is cited in At the Mountains of Madness. (Pearsall, "Poe, Edgar Allan", The Lovecraft Lexicon, p. 332.)