Great Old Ones' universe

By many accounts, the powerful beings known Great Old Ones originated in another universe than the Doctor's.

This universe was various identified as an ancestor-universe which had existed before the Big Bang, (PROSE: Millennial Rites, Synthespians™, Divided Loyalties; AUDIO: The Key To Key To Time) or simply as a parallel universe, possibly one of "the outer planes", which coexisted with the Doctor's and from which the Great Ones had simply come as conquerors. (PROSE: White Darkness)

Additionally, one account suggested that the Great Old Ones' home reality, spoken of in The Book of the Old Time as the 'space before this, was not actually a distinct universe but simply the time before this, Old Time or Dark Times which predated the anchoring of the thread. (PROSE: Christmas on a Rational Planet, The Book of the War, AUDIO: The Magic Mousetrap) This reality had different physical laws, more based in magic, which gave its survivors great power in other realities. (PROSE: Millennial Rites, Synthespians™, Divided Loyalties) This perspective viewed the 'previous universe' hypothesis as a misunderstanding of the truth arising from small-mindedness. (PROSE: Christmas on a Rational Planet) A similar but distinct account indicated that the reality from which the elder races originated was actually the original palimpsest universe. (PROSE: Mr Saldaamir)

Creation
According to The Record of Rassilon, this universe most likely had prior ancestor-universes before it, including that of the Gods of Ragnarok, who had destroyed the universes before this one. These Gods survived into the newborn universe as powerful beings. (PROSE: Divided Loyalties) The Seventh Doctor believed that this universe existed as part of the cyclical nature of the universe, which periodically went through cycles of expansion and contraction punctuated by Big Bangs. (PROSE: All-Consuming Fire)

Existence
A set of physics developed which was based on quantum mnemonics. The heavens were green and the stars looked like giant doughnuts. Time was "strange".

An equivalent of the Time Lords emerged, and came to rule this universe via magic. (PROSE: Millennial Rites) They were far more advanced and evolved than the Time Lords of the Doctor's universe. (PROSE: Divided Loyalties) Yog-Sothoth was their military strategist. (PROSE: Millennial Rites)

Destruction
This universe was destroyed by the Gods of Ragnarok. (PROSE: Divided Loyalties) Furthermore, River Song believed that the previous universe had been wiped out by a war. (AUDIO: Signs)

As the universe reached a point of collapse, a group of its Time Lords briefly shunted themselves sideways into a parallel universe which ended a split-second later, thereby allowing themselves to survive the Big Bang and return to the newly-created N-Space. (PROSE: Millennial Rites, All-Consuming Fire)

According to the Sixth Doctor, the Toymaker originated in another universe before the Doctor's and was hauled into the Doctor's universe by some kind of catastrophe. (AUDIO: The Nightmare Fair)

This universe and its replacement were forever separated by a point where time and space didn't exist. (PROSE: All-Consuming Fire)

Legacy
The survivors of this universe became the Great Old Ones, powerful because the usual laws of physics didn't apply to them. According to The Toymaker, they initially used their powers for other things in the beginnings of the universe, but some eventually got bored of thousands of millennia of pointless creation and pointless destruction and turned to other things. (AUDIO: The Nightmare Fair)

The Time Lords had records of "the universe before theirs" in the Matrix, which the Sixth Doctor accessed in the Matrix during his time as Lord President. He later described it to Anne Travers. (PROSE: Millennial Rites)

The Warrior knew that the Old Ones in the Wilderness Beyond Time came from the universe before his own. (AUDIO: The Key To Key To Time)