The Great Old Ones are a pantheon of malevolent entities in the Doctor Who universe. The first time appearance of the Great Old Ones of the Cthulhu Mythos in Doctor Who was in the 1993 novel 'White Darkness by Virgin Publishing, with Cthulhu as the primary antagonist. In 1994-1995, old enemies of the Doctor (e.g. Animus) were retconned into Great Old Ones in the novels "All-Consuming Fire" and "Millennial Rites".
The Great Old Ones are entities which existed before the universe. Beings whom in the race memory of mankind, were it's worst nightmares. Entities that spread chaos, evil, and destruction wherever they were. They couldn't be killed within the material universe. The language of the Old Ones was quantum mnemonics which was their equivalent of Block Transfer Computations, giving them the ability to rewrite reality. They saw the Time Lords as a threat.
In their home universe, the Old Ones had physical bodies. When they entered N-Space, they got new bodies and some of them lost their new bodies when forced to flee from the Fendahl, abandoning their new forms. Afterwards, for brief periods of time the Old Ones were able to assume physical forms, as their new state of being as that of collective consciousnesses. The Old Ones created planes and universes between the dimensions, which became their new home. The Old Ones could not die within the material dimension, simply reappearing if killed. The reason being that their bodies were composed of energies that didn't belong in the material universe. If they decayed, those energies would tear apart space and time. They only place that an Old One could safely die was either in it's own universe or the Board, causing the Time Vortex to turn inside out. TARDIS sensors revealed that the amount of energy in an Old One's body was the equal of 20 billion nukes.
It's theorized that the Old Ones were the Time Lords of their universe. The Great Old Ones whom were most active in the universe were known as the Elder Gods, whom played cosmic games with each other, using the dimension known as the Board. The powers displayed by the Great Old Ones varied depending on the individuals including the re-animation of the dead, extending individual's lifespan, time travel, manipulating and relocating timelines, creating thunder and lighting, simultaneously existing in multiple time zones, stopping a TARDIS in fight, and generating fog/fungus and webbing.
Deviation from Canon
In the Doctor Who universe, there are no Outer Gods. Entities which in the Cthulhu Mythos (e.g. Yog-Sothoth) are Great Old Ones, not Outer Gods. Though beings of great power they were rivaled by the Chronovores and Eternals. The greatest powers in the universe were races with godlike technology, the Time Lords and the Daleks.
Known Great Old Ones
- The Great Intelligence
- Nestene Consciousness
- Guardians of Time
- Celestial Toymaker
- Gods of Ragnarok
- Gog and Magog
- Mi'en Kalarash