Great Old One

The Old Ones, sometimes known as the Great Old Ones, were beings from before the universe, according to the Doctor. (NA: White Darkness, All-Consuming Fire, MA: Millennial Rites)

History
Folowing the demise of the last universe, they passed on into this one in which they discovered they had god-like powers with which they manipulated the universe. (MA: Millennial Rites)

At one point they attempted to enter into the higher dimensions by using the Palace of the Old Ones to power a gateway. One of their number, known as Valdemar, discovered that his kind were unprepared for the perceptions of this new reality and were being driven mad by it. This breach would have destroyed the universe had Valdemar not sacrificed himself to seal the breach. Legends would spread across the galaxy that he was a dark god that nearly destroyed the Old Ones though the truth was far different. (BBC: Tomb of Valdemar)

Ancient carvings show that the Old Ones escaped some great cosmic disaster in order to flee into the Time Vortex where they became discorporate entities thus leaving their bodies behind. They have sought to return ever since. (NA: White Darkness)

The Pharoah Amenhotep discovered them at one time on Earth and attempted to harness their power for himself. However, he came to realise that they were beyond his control and lured them into a white pyramid with a structure of infinite reflections where the creature's evil were to be trapped forever. This trap succeeded and kept the world safe from their evil. (BFA: The Roof of the World)


 * The appearance and powers of the Old Ones vary from entity to entity. They all have, in Human terms, immense powers.

Overview
The Great Old Ones were unimaginably ancient creatures that were preserved in Humanity's race memory as their worst nightmares. They were concieved as creatures that spread evil, chaos and destruction in their wave wherever they went. (BFA: The Roof of the World)

Quantum mnemonics was known to be the language of the Old Ones as they represent physical laws of the Universe that preceded the current one. This allowed it to rewrite reality on the most fundamental of levels. (MA: Millennial Rites)

List of Old Ones by their Mythos names

 * Azathoth
 * Cthulhu
 * Dagon
 * Hastur the Unspeakable
 * Lloigor
 * Nyarlathotep
 * Shub-Niggurath
 * Yog-Sothoth

Other described as Great Old Ones

 * Magog
 * Na
 * Rag
 * Ok

Behind the Scenes
The Old Ones originated out of the Cthulhu Mythos, a shared universe based on the writing of H.P. Lovcraft and to an extent, some of his contemporaries. A few characters and concepts in televised Doctor Who, such as Sutekh (though based on an actual ancient Egyptian god) and the Fendahl, had shown the apparent influence of the Mythos. However, not until the novels White Darkness, All-Consuming Fire and Millennial Rites did beings explicitly referred to as Old Ones appear in fiction set in the Doctor Who Universe.

The latter two books took known Doctor Who enemies, such as the Animus and retconned them into having links to the Mythos. The Taking of Planet 5 revealed that the Cthulhu Mythos also existed in the form of fiction in the Doctor Who Universe. Though the established Cthulhu Mythos and the Doctor Who version have some differences (the idea of the Old Ones originating before the universe originates in Doctor Who novels, for example), stories set in the Mythos frequently contradicts itself.