Old One (The Knight, The Fool and The Dead)

According to one account, "Old Ones" was a name used during the Doctor's education for the most powerful species of the Dark Times. He had read of their "rise", which was to be contrasted with the generally peaceful demeanour of most species of their era.

In their heyday they were "giants of the universe", but, by the time the Doctor crossed paths with them, all of them had been reduced to mere "remnants". Among those late-surviving Old Ones were the Exxilons, the Eternals, the Jagaroth and the Racnoss. (PROSE: The Knight, The Fool and The Dead)

Eternals
The Eternals, as their name suggested, had eternal lifespans. The first event that they were known to have been involved in was to banish the Carrionites and Hervoken into the Deep Darkness during the Dark Times of the Universe. (TV: The Shakespeare Code, PROSE: Forever Autumn) On Earth, they could be recognised as gods, angels, earth spirits, devils, demons, ghouls, and poltergeists. (PROSE: Blood Harvest)

Some of the Eternals passed themselves off as Gallifreyan deities, the Menti Celesti, such as Time, Pain and Death, a development which Lady President Romana II found distressing. (PROSE: Happy Endings) Not all Eternals did this, and until he met the Fifth Doctor and probed his mind, the Eternal known as Striker professed that he had never heard of the Time Lords. (TV: Enlightenment)

A temporal skirmish opposed the Eternals to the Halldons, but an end was brought to it by the Time Lords, in one of the very few time wars they would fight prior to their great War with the Daleks, (PROSE: Meet the Doctor) the, by a dissenting account of their history that disagreed with the stories of Yarvelling or Davros, rebellious creations of the Halldons. (PROSE: We are the Daleks!) During the Last Great Time War, the Eternals finally forsook the universe, (PROSE: A Brief History of Time Lords) abandoning their "hallowed halls" as they "despaired" of this reality. (PROSE: Meet the Doctor)

Exxilons
The Exxilons were an ancient species, apparently capable of space travel before life had formed on other worlds. They travelled throughout the Mutter's Spiral and were reportedly the most powerful species in the universe, at least for a short time. (TV: Death to the Daleks, PROSE: Death to the Daleks) At the height of their power, they influenced the development of other early civilisations, including the Earth. (TV: Death to the Daleks, PROSE: Death to the Daleks)

They were one of the species involved in the Millennium War, joining forces with the Uxarieans to fight the minions of the Mad Mind of Bophemeral in the Andromeda Galaxy. They were both caught in a trap that led to their eventual downfall and the creation of the Crab Nebula. (PROSE: The Quantum Archangel)

Eventually, the Exxilons decided to pool their knowledge and create the Great City of the Exxilons. It combined all of the science known to the Exxilons and was intelligent and capable of repairing itself. During this time, the Exxilons would travel to other inhabited worlds where they would construct great beacons on their surface that would drain the mental energy of the natives and send it back to the Great City. (AUDIO: The Exxilons) Eventually, the City decided that the only flaw left was the Exxilons themselves and it drove them out. The City drained all the energy from the planet, which meant the Exxilons were incapable of developing any technology above the stone age. They slowly descended into a primitive species. (TV: Death to the Daleks)

During the space plague at the end of the Third Dalek War, (PROSE: The Secret Lives of Monsters) humans came to Exxilon in search of parrinium. Their ship failed as soon as they reached the planet, and they were attacked by the primitive Exxilons as soon as they arrived. They tried to survive on the planet, but the Exxilons were a permanent danger. Shortly afterwards, the Third Doctor and Sarah Jane Smith came to the planet by accident, and Sarah was kidnapped to be sacrificed. Before the Doctor could do anything about it, the Daleks came to the planet, looking for parrinium which they could use to threaten the Earth colonies. They too were de-powered by the City, but after several defeats, they were able to modify their weapons, allowing them to fight back. They enslaved the surface Exxilons and forced them to mine the parrinium. While escaping from the Daleks, the Doctor and Sarah Jane encountered the underground Exxilons. The Doctor helped one, named Bellal, find a way into the City and destroyed it from within. (TV: Death to the Daleks)

Racnoss
The Racnoss evolved in the Dark Times of the universe. (TV: The Runaway Bride, The Infinite Quest) When the Kotturuh stood in judgement over the Racnoss, they judged them not to be a "particularly useful" species and thus cursed them with mortality. (PROSE: The Guide to the Dark Times) They were nearly wiped out by the Fledgling Empires (TV: The Runaway Bride) in the Racnoss Wars (AUDIO: Empire of the Racnoss) over 4.6 billion years BC. Gallifreyans also had a hand in this. Another source posited that the Racnoss ate each other to near extinction, at least according to the Matrix. (PROSE: Doctor Who and the Krikkitmen)

Nearly all of the survivors of the race escaped in their spacecraft, around which the planet Earth would later form. An Empress of the Racnoss stayed in her Webstar, but also went into hibernation at the edge of the universe until she decided to search for her young. Around 2007, the Torchwood Institute began a drilling attempt to the centre of the Earth. This awoke the Secret Heart, which in turn signalled the Empress of the Racnoss. She came to Earth and used Huon particles manufactured from the River Thames to feed Donna Noble with the right catalysis of particles to awaken her young. The Doctor killed the Racnoss young by flooding the tunnel to the centre of the Earth with water from the Thames while the Empress teleported back to the Webstar plotting revenge. However, she had used up all of her power to attack London and revive her children and was left defenceless to a tank attack ordered by which destroyed the ship and killed her, rendering the Racnoss extinct. (TV: The Runaway Bride)

Jagaroth
At some point in the distant past, following the era of the Fledgling Empires, the Jagaroth had constructed a massive interstellar empire only for it to grow beyond their ability to control. When their subjects rose up against them, the Jagaroth were reduced to only one ship. (PROSE: The Whoniverse) This ship made it to the primordial Earth, having tracked a Racnoss energy signal, (PROSE: City of Death) four hundred million years prior to the 20th century, (TV: City of Death) due to the presence of the Empress of the Racnoss and her brood having hidden at the centre of the Earth earlier still in its history. (TV: The Runaway Bride)

Finding it unsuitable for habitation, they planned to leave the planet. However, their atmospheric thrust motors were damaged and inoperable, and they decided to take off using their warp-drive, against the advice of Scaroth, their warp-field operator. The attempt to do so deep failed, and the ship exploded. The massive burst of radiation generated by this explosion catalysed the development of life on Earth.

It also propelled Scaroth into the Time Vortex, where he splintered into twelve incomplete aspects of himself, each trapped at different points in the timeline of Earth. These aspects of Scaroth pushed forward the development of humanity, so that technology sufficiently advanced for time travel could be created and he could return to stop his past self from entering warp drive, and in turn save his people. He was eventually able to travel back in time to the moment before his ship's explosion, but was stopped by the Fourth Doctor, Romana II, and Duggan. After the latter knocked him unconscious, Scaroth was returned to 1979, where he was killed by his servant Hermann, in turn destroying the time field. This allowed the creation of life on Earth to go unaltered, and brought about the extinction of the Jagaroth. (TV: City of Death)