A Great Old One, or collectively the Great Old Ones, is a type of extraterrestrial beings of immense power, and most are also colossal in size. These entities seem to have a physical shape, but being cosmic lifeforms from beyond our space-time continuum means they are not based on matter in our definition of the concept, yet their forms are built on principles similar enough to those of true matter that they appear to be material in their nature. They are worshipped by deranged human cults, as well as by most of the non-human races.
The Great Old Ones hailed from the realm of Yuggoth and made first contact on Earth since the dawn of time, in which they confronted and battled the Elder Gods. Eventually, the Great Old Ones were either banished from the planes of existence, or else magically imprisoned in empowered locations such as R'lyeh. However, during their tenure on Earth, the Great Old Ones both interbred between themselves and also to have sired a great variety of half-breed monsters on the human populations, such as Tibet's Tcho-Tcho people, or the fish-like Deep Ones. Despite their imprisonment, the Old Ones were able to exert their influence and to command multitudes of worshippers both human and non-humans, which survived to the 20th Century.
- Azathoth - Nuclear Chaos, the Daemon Sultan and the Blind Idiot God.
- Cthulhu - the Sleeping God
- Nyarlathotep - the Crawling Chaos
- Shub-Niggurath - "The Black Ram of The Forest With A Thousand Ewe"
The Great Old Ones are based in the Cthulhu Mythos stories of H. P. Lovecraft. Though Lovecraft created the most famous of these deities, the vast majority of them were created by other writers, many after Lovecraft's death. Collectively, the Great Old Ones (sometimes referred to as the Old Ones by some authors or the Cthulhu Cycle Deities by Brian Lumley in his Titus Crow stories) are not as powerful as the Outer Gods, nor do they have as much influence. Nonetheless, they are served in the stories by devoted congregations of worshippers, made up of both human and non-human cults.
- Great Old One on Wikipedia