The Six

The Six was the main alias used by the sixth incarnation of a Renegade Time Lord who suffered from regenerative dissonance.

Post-mortem
The Six urged the Nine to kill Padrac, Liv Chenka, "the Clocksmith" and "Sister Cantica". The Nine said that, for once, they were in agreement. (AUDIO: The Crucible of Souls)

When Liv Chenka called the Nine a psychopath, he corrected her, saying that he was just a kleptomaniac and that the psychopath was "three regenerations back". Angered by River Song's plan of escaping, the Nine considered letting the Six "off the leash". The Six, in turn, found the Nine's torture of River, Liv, Helen, Charley and Bliss to be "fun". (AUDIO: Companion Piece)

The Eleven threatened to unleash the Six upon. The Six said that he would be happy to "eviscerate him". (AUDIO: The Side of the Angels)

The Six said that he wanted to kill Helen Sinclair from the moment that he met her. (AUDIO: Stop the Clock)

On Parrak, when confronted by the Eleven wondered which incarnation he was in, dismissing the Six instantly. (AUDIO: Planet of Dust)

When trying to guess the identity of, Liv believed him to be the Six. (AUDIO: Day of the Master)

At some unknown time, the Time Lords decided that removing one of the Eleven's personalities would make him more controllable. They had intended to remove the One and place him inside the Sand Box. Instead, the Six took his place, and was removed instead. However, the prison was not designed to house part of a mind, enabling the Six to move about the prison, looking into the minds off all the prisoners. Omega learned of "the One's" imprisonment, and decided that he would be perfect to work with. He forced the Master to work for him and help engineer the opening of the Box, releasing all the prisoners inside. The Six, however, was obsessed with getting a body of his own and killing the Doctor. It took both the Third Doctor and the Fourth Doctor, along with two versions of Sarah Jane Smith, to stop both Omega and the Six and seal them both, along with all the other prisoners, back into the Sand Box. Some time later, the Eleven discovered where the Sand Box was and went there to retrieve his missing persona, having decided that life was less fun without him. (AUDIO: The Box of Terrors)

When the Twelve tapped into her old personalities, the Six threatened her and the Eighth Doctor. The Twelve made her sixth incarnation apologise, and described him as a "horrible little man". (AUDIO: Planet of the Ogrons)

When the Doctor broke the Twelve's neural inhibitor whilst she was holding the Panopticon hostage with a Dreadshade, the Six emerged and delighted in the situation. (AUDIO: Dreadshade)

Personality
The Six was extremely violent and also very unstable. He would often try to get his future incarnations to butcher their way through a situation, regardless of whether the victims could be of use. (AUDIO: The Eleven, Companion Piece) The Eighth Doctor described him as a psychopath, (AUDIO: Planet of the Ogrons) as did the Nine himself. (AUDIO: Companion Piece)