Glaaki

Glaaki (also spelled Gla'aki) is an extraterrestrial entity, and the central figure in a 19th century cult documented in the infamous grimoire called The Revelations of Glaaki. It inhabits a lake in the Severn Valley, England, which is actually the impact crater formed from the meteorite that brought it to Earth from its unknown cradle in space.

Although it doesn't seem to leave the confines of the lake physically, Glaaki can manifest itself in the dreams of nearby Humans, and uses this ability to attract victims to the lakeshore (a process known as "dream-pull"), at which point the monster surfaces and attacks with its toxic spines that turns the victims into zombie-like servants, mentally controlled by Glaaki.

Biology
The cellular structure of Glaaki's body is metallic; based on what has been described as a "living, iridescent metal", unlike any substance found on Earth. Its shape is reminiscent of a giant oval slug, whose mantle is covered in long, thin, metallic, multi-colored, detachable hollow spines. These are used to perforate victims and inject them with Glaaki's venom, which turns them into nearly-mindless slaves and allows them to be controlled by Glaaki.

The underside of Glaaki's body is covered in white pyramidal structures, which aid in locomotion. It has a circular mouth with thick lips, and three yellow eyes held on top of long sinuous eyestalks. The diameter of its oval-shaped body is estimated as about 10 feet (3.048 meters).

Glaaki's servants
The scars left by the beast's spines when they perforate a Human victim become what has been traditionally referred to as a "witch's mark": a small area of the body that will never bleed when perforated, and can be used to identify "witches", or in this case Glaaki's servants.

Humans who have been infected by Glaaki's venom live for the next 65 years with no large physical changes, and retain some level of free will when not under direct orders from their master. After 65 years, however, they fall victim to what's been called the "Green Decay", which makes their bodies frailer and incapable of withstanding sunlight.

History
Glaaki's age isn't known for certain, but there's no doubt about it being an ancient entity which was present on other worlds such as Yuggoth, Shaggai and Tond before settling down on Earth via a meteorite impact that created the lake it currently dwells in.

Appearances

 * "The Inhabitant of the Lake", by Ramsey Campbell (1964)