The Eight was the main alias used by the eighth incarnation of a Renegade Time Lord who suffered from regenerative dissonance. Unlike his other incarnations, he attempted to be a "good man". Using meditation, he was able to suppress the voices of his previous incarnations.
As a physical being Edit
In 14th century Prague, the Eight witnessed the Clocksmith and the Solvers collecting the Syran metal deposited by the Eleven's TARDIS and claimed that the end of the universe was upon them. The Clocksmith had a duke imprison him in Prague Castle as he would not support the Doom Coalition, although he eventually managed to escape. During this time, he was referred to as Osm by his jailors.
By 1538, the Eight was living as Brother Octavian in an English monastery where he was taught to deal with the voices in his head by Abbot Malvern. Upon seeing the Eighth Doctor, he ran away, but later told the Abbot to make sure that the Doctor did not interfere in the matter of the Chronometer. (AUDIO: The Eighth Piece) He sent the Doctor's TARDIS to the Tower of London and, after he left with Lady Risolva, wrote a report of the Doctor's death for Thomas Cromwell.
Stowing away in the Clocksmith's TARDIS, the Eight arrived in 2016 Rome and saved Helen Sinclair from walking into the road. He went to the Science Museum to stop her from completing the Chronometer and met the Doctor and River Song, launching a psychic attack against the Clocksmith. However, the Clocksmith attempted to kill the Eight, who later climbed from the rubble and regenerated into the Nine in the Doctor's TARDIS. (AUDIO: The Doomsday Chronometer)
Post-mortem activities Edit
When the Eleven made a deal with the citizens of the Dark Universe to control the universe, he transferred his other selves into robot bodies. The Eight persona was reduced to the role of cleaning the Eleven's palaces, but this put him in a position to help Ace, Cardinal Ollistra and Captain Rasmus when they came to defeat the Eleven, the Eight using his cleaning solution to neutralise the other soldiers and lead them to the Dark Gate so that they could convince the Dark Citizens to withdraw (AUDIO: Dark Universe).
The Eight said that there was no need after the Eleven shot and killed a man and warned Joanie Carrington to leave her date with the Monk so that the Eleven would kill her. The Doctor managed to convince some of the Eleven's previous selves that Padrac and the Sonomancer did not want him and the Eight activated his Time Ring to send the Eleven back to Gallifrey. (AUDIO: The Side of the Angels)
As a thriving persona inside the Eleven's consciousness, he successfully took control of his physical body and told the Doctor about Padrac's plans to use the Resonance Engine as a means to amplify Caleera's powers. (AUDIO: Stop the Clock)
When the Eleven acted to undermine the Nine's plan to use the Ravenous to kill the Doctor, Liv and Helen, the Eight assumed that he had "seen the light", but the Eleven coldly corrected his predecessor that he was only sparing them now in order to deliver a more devastating blow later. (AUDIO: The Odds Against)
When the Eleven was pretending to have been 'cured' of his condition after an attack by the Ravenous, he occasionally allowed the Eight out to give the impression that Eight was helping him keep the others in check, the other nine personas threatening to bury the Eight in their subconscious for good if he didn't go along with the lie (AUDIO: Whisper, Planet of Dust)
While the Twelve discussed her previous selves with the Doctor, who referred to the previous personas as "a mad stew of voices and personalities" who were all "mad and homicidal", she thought the Doctor was being unfair on the Eight, whom she described as "sweetness itself". The Doctor then conceded, and described him as "the exception that proved the rule". (AUDIO: Planet of the Ogrons)