Originally, Lloigor was a Great Old One created by August Derleth, said to be the twin of Zhar and child of Shub-Niggurath. The mythos race first appeared in Derleth and Mark Schorer's short story "The Lair of the Star Spawn" (1932).
The lloigor are an alien species that feature in Colin Wilson's story The Return of the Lloigor. They are invisible "vortices of energy," but can take monstrous, reptilian physical forms. They came to Earth and settled on the continent of Mu which existed between twenty thousand and twelve thousand years ago.
On Mu the lloigor kept human slaves to feed off of. The lloigor have a unified mind, not like human compartmentalized minds, were naturally pessimistic. Because of this and it's clash with Earths more upwards moving evolution the species have to feed on optimistic energy of people to survive. It is unknown why the lloigor left their original home somewhere in the Andromeda nebula, but the Earth's nature is hostile to them. Nowdays they are only really powerful below ground.
Arthur Machen's stories based in Wales have certain connections to the lloigor who may now live there. He describes certain idiot families who breed with unknown evils, this has been connected to the lloigor.
The lloigor have the power to manifest themselves and cause huge explosions, one of these caused the destruction of Mu itself. The destruction of many other cities and locales have also been attributed to them, including in The Mysteries of Mu the grand canyon. These eruptions or rains of fire are said to leave behind strange greenish lakes of contaminated water, of which many can be found around the world. This "explosion" may in fact be the lloigor clawing their way out of the Earth causing earthquake like destruction, then physically tearing the area, and any inhabitants apart. The hole left behind then is filled with water causing the green lakes.
The main power of the lloigor is to drain energy from their victims causing depression and violent tendencies. According to The Mysteries of Mu this proves that the Welsh people are descendants of the human slaves of the lloigor, and that the Welsh serpent is one of these creatures.
The lloigor also have incredible powers of surgery, they are able to detach limbs completely and keep their victims alive. They can also cause tentacle like blisters to grow on their victim's bodies. They use this to control their hosts. The Naacal Tablets show drawings of victims with tentacle blisters growing from both eye sockets.
Because the lloigor are normally immaterial they can manipulate objects, this would appear as if the objects were moving of their own accord. They can also touch humans if they want and will attempt to hurt those who might reveal their existence. Pushing victims down stairs or tripping them up are definite possibilities. They could also demagnetize compass needles, or affect other objects of matter. They are most powerful when underground, or in hollows.
The lloigor can also appear as a large reptile.
- Wilson, C. P. "The Return of the Lloigor." Tales of the Cthulhu Mythos. New York: Ballantine Pub. Group, 1998. N. pag. Print.