Eternal

The Eternals were beings of immense power but limited creativity. They used the thoughts and emotions of so-called Ephemerals for their own ends.

Characteristics
The amoral Eternals made it their principal aim in life to amuse themselves, using Ephemerals as their toys. (TV: Enlightenment) In the course of their games, the Eternals would sometimes pose as gods and doom whole worlds in the process. (COMIC: Uninvited Guest) These games were started by the Guardians of Time, whom the Eternals greatly respected as leaders. (PROSE: The Quantum Archangel)

Though they were related to the Chronovores, they looked down on them as vicious predators. The Ancient Covenant prohibited a union between the two races. However, the great Kronos arose from one such union. (PROSE: The Quantum Archangel)

Through somewhat obscure means, as a punishment, the Seventh Doctor used the force of the Time Vortex itself to bring the particularly callous Lord Prospero and his social circle into the domain of Time, which would indicate that under some circumstances they could transition from Eternal to Ephemeral. (COMIC: Uninvited Guest)

Powers
The Fifth Doctor called Eternals parasites for using Ephemerals for their creativity, as Eternals could pull any being from any planet in any time and use them. The Eternals dwelt in the domain of Eternity rather than the smaller one of Time. This meant they were unaffected by Time and thus unaging. They could even freeze Ephemerals in time. Eternals could not be destroyed, only transferred. They could use telepathy and create objects from the memories of Ephemerals, but their powers were not limitless and they could not read minds from great distance or from strong minds. Eternals could also concentrate and channel great power (in one case, power from the Black Guardian) but only if there was a focal point. (TV: Enlightenment) They could also appear in dreams. (PROSE: Love and War)

History
The Eternals were, as their name suggests, eternal, therefore a history of their race would be hard to find. However, the first event that they are 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)

Some of the Eternals passed themselves off as the Gallifreyan deities such as Time, Pain and Death, a development which Lady President Romana 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)

At some point, the Guardians of Time set up a race for a group of Eternals, with Enlightenment being the prize. Groups of Eternals copied ships from various points in Earth's history, fitted them with ion drives and sails to catch solar winds and kidnapped humans to run the ships. Though Captain Wrack almost won the race by destroying the ships of her enemies, the Fifth Doctor managed to push her off her ship and bring it to the Guardians of Time. (TV: Enlightenment)

The Monk used the blood of an Eternal he had met in Paris to trap Artemis. (PROSE: No Future)

The Tenth Doctor warned the Hervoken to beware of attracting the Eternals' attention. (PROSE: Forever Autumn)

In 2604, Bernice Summerfield became caught up in the conflict between the Eternals Raymond Hardy and Barron. (AUDIO: The Heart's Desire)

Other information

 * The Eternals referred to the Void as "the Howling". (TV: Army of Ghosts)
 * Sebastiene claimed to have hunted down an Eternal. (PROSE: The Doctor Trap)
 * Adam, an alien who infiltrated Torchwood Three, showed powers similar to those of an Eternal, and also said that he had escaped from the Void. (TV: Adam)
 * It is possible that the Trickster was an exile of the Eternals. (TV: The Wedding of Sarah Jane Smith)

Behind the Scenes

 * According to to REF: Doctor Who Annual 2006, a non-narrative source, there had been a war between the Halldons and the Eternals, and that the Time Lords had intervened to stop it.