Earlier race of Time Lords

Some accounts suggested that the "group of beings" who survived the destruction of their own universe, which existed before the creation of the Doctor's universe in the Big Bang, and became the Great Old Ones (PROSE: All-Consuming Fire) or elder gods, were originally an "earlier race of Time Lords", the Time Lords of that universe just as the Doctor's people were the Time Lords of their own reality. (PROSE: Millennial Rites, Divided Loyalties) Though they would have called themselves Time Lords as well in their original reality, the Doctor only called them such in quotation marks, as they had been Lords of "a very strange version of time and space" indeed. (PROSE: Millennial Rites)

"In the dying days of the universe before this current one, which is forever separated from us by a point where time and space do not exist, a group of beings discovered how to preserve themselves past that point where their universe ceased. They shuttled themselves sideways, into a parallel universe which, for various reasons that I will not even attempt to explain now, ceased a split-second after our one. (…) Just before that universe ceased, they jumped back to our one, which had just started expanding afresh after a moment of nothingness. The trouble is, the universe before ours was set up differently. Fundamental physical laws such as the speed of light and the charge on the electron were different, which means that the Great Old Ones have powers undreamed of by anybody in this universe. Powers that make them look like gods, to naive races."

- Seventh Doctor (PROSE: All-Consuming Fire)

Yog-Sothoth, later known as the Great Intelligence, was the military strategist of these "Time Lords". Others of this race, reborn in monstrous bodies made of pure energy which couldn't fully exist in three-dimensional space included Lloigor, whom the Doctor identified as (PROSE: Millennial Rites) the Animus of Vortis, (TV: The Web Planet) and Shub-Niggurath, whom the Doctor identified as the mother of the Nestene Consciousness on the planet of Polymos. Yog-Sothoth stayed in contact with them, and they mocked him for his lack of success with the "war games" he played in various planets in the universe, including (PROSE: Millennial Rites) his attempts to conquer Earth using Robot Yeti. (PROSE: Millennial Rites, TV: The Abominable Snowmen, The Web of Fear)

According to one account, Rassilon studied these interlopers, coming to suspect their origins as the Time Lords of another, destroyed reality. He was the one who named them "Great Old Ones", and also gave them individual names to give future Time Lords power over them. In addition to Yog-Sothoth, Loigor and Shub-Niggurath, his list included Hastur, (PROSE: Divided Loyalties) whom the Seventh Doctor stated was the true identity of his enemy Fenric, (PROSE: All-Consuming Fire) as well as Cthulhu, (PROSE: Divided Loyalties) identified by the Seventh Doctor as the Old One he had fought in 1915 Haiti, (PROSE: All-Consuming Fire, White Darkness) Tor-Gasukk, Gog and Magog, Nyarlathotep, Dagon, and Melefescent. (PROSE: Divided Loyalties) He also cited the three Gods of Ragnarok, Raag, Nah and Rok, whom he believed responsible for the destruction of the Old Ones' original universe.

Additionally, Rassilon wondered if the Guardians of Time were simply powerful Great Old Ones, or an even greater, more primordial class of entity. The Black Guardian and White Guardian refused to answer when he met them, but the Sixth Doctor later believed the Guardians to indeed be the "upper echelons" of the Great Old Ones from the old universe, something he repeated to another Guardian without being contradicted. (PROSE: Divided Loyalties)