Your Cthulhu Mythos Cheat Sheet Part 1.

I often end up babbling on and on about H.P. Lovecraft's Cthulhu Mythos to people whom haven't actually read a Cthulhu Mythos story and may indeed think H.P. Lovecraft is a sex shop that also sells printers.

Given that Lovecraft's cosmic horrors have infected pretty much every area of pop culture since his death in 1937, herewith a short glossary to help you navigate those rare occasions when you suddenly need to pretend that you know the difference between a Shoggoth and Fungi from Yuggoth.
　
H.P. (Howard Philips) Lovecraft 1890-1937: New England born-and-bred writer of science fictional horror and fantasy, he wouldn't become really famous until decades after his death from stomach cancer. A mentor to such writers as Robert E. Howard (creator of Conan) and Robert Bloch (creator of Psycho). Quite racist and classist -- many of his horror stories showcase a profound fear of miscegenation and/or the 'lower' classes. Cthulhu Mythos term actually coined by Lovecraft's posthumous Boswell August Derleth, who founded one of the greatest genre specialty publishing houses, Arkham House, in part to keep Lovecraft's fiction and poetry in print. Central conceit of Cthulhu Mythos is that all religion is wrong, and that Earth was once the home to various cosmic beings who want to get back in but are blocked from doing so for the present. Humanity itself appears to have been some sort of lab accident.

Those crazy names: The names of alien beings in Lovecraft are ostensibly, for the most part, approximations and not 'authentic,' primarily because creatures such as Cthulhu have much different vocal and auditory apparati than human beings.
　
Great Old Ones: Blanket term for ancient alien beings who want our planet back, including Cthulhu.

Yuggoth: Pluto.

Elder Gods: Blanket term for never-seen alien race that opposed the Great Old Ones long ago and managed to expel them from our space-time and bar them from returning. Apparently exist in or around the star Betelgeuse.
　
Cthulhu: Ancient and extremely powerful alien being who's either from another dimension or just from somewhere else in space. Changes in space and time, either accidental or engineered by the ELDER GODS, have barred Cthulhu from Earth, where he used to hang out and get up to all sorts of mischief. He will, however, eventually break back into our planet and lay waste to everything we know. Looks like a cross between a mosquito, a squid and a biped; seems to be about as big as a fair-sized office building. Sort of lives on an island submerged in the South Pacific which periodically rises when conditions become right for Cthulhu's re-emergence. Last recorded re-emergence thwarted when a sea captain rammed Cthulhu with a yacht in the 1920's, keeping Cthulhu in the vicinity of the island (Ry'l'yeh) just long enough for conditions to change to force Cthulhu to return to the island before it submerged again.

Dagon: Cthulhu's lieutenant in the Atlantic Ocean; named for Sumer-Babylonian sea-god.

Yog-Sothoth: Cthulhu-level being that seems to act as the gatekeeper (or gatecrasher) between our world and Theirs. Seems to be stuck in 'our' space somewhere around the demon-haunted New England town of Dunwich. Can get human women pregnant. Apparently looks like some sort of tentacle-waving, many-faced blobby thing.

Azathoth: Insane or possibly mindless central being for Cthulhu-type beings, may actually be the center of all existence. Enjoys flute music and weird, shrill piping.

Nyarlathotep: Messenger and harbinger of the Cthulhu-type beings, can occasionally appear as human, but normally looks like some sort of multi-headed flying creature with a "three-lobed burning eye." Can operate in our world under certain conditions, but is extremely sensitive to even small levels of light.

Shub-niggurath: Also known as the "Goat with a Thousand Young", is roughly an Earth Elemental to Cthulhu's Water Elemental. Extremely blobby looking and, under the right conditions, capable of spawning miniature versions of self. Seemingly confined somewhere in England.

Old Ones: Powerful alien beings at war with Cthulhu and company. Once lived on Earth tens of millions of years ago, building a great city at what is now the South Pole, among other places. Final fate of entire species unknown. Ill-fated Miskatonic University expedition to the Antarctic Mountains of Madness in the 1930's unearthed several Old Ones which returned to life once they were thawed and, in a panic, killed most of the expedition before travelling to their seemingly empty city. Resemble seven-foot-tall winged sea-anemones with starfish heads; some sort of animal/vegetable hybrid.

The Mi-Go: Winged, mothmen-like aliens who are enemies of the Old Ones and servants of Cthulhu. May be carrying on mining operations in the Vermont hills for some unknown substance to this day. Can 'fly' through space and enjoy keeping human brains alive and communicative in large metal holding tanks. Are more closely related to fungus than animals. Hail from beyond our solar system, though they do have a base on Pluto (a.k.a. Yuggoth). Can be killed by floods, rifle fire and dogs. Source of stories of the Yeti/Abominable Snowman, as the Mi-Go prefer to stay on or near mountaintops when on Earth.

Shoggoths: Shape-changing, acid-spewing, multiple-mouthed former servants of the Old Ones and current servants of the Great Old Ones. Can live on land or in water. While there's a major hive of them in the city of the Old Ones in Antarctica, they also live throughout the world's oceans and have been seen in New England. Can be as large as the passenger car of a train.