The Two

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

Trying to stop his future
After regenerating for the first time, the Two found out he suffered from regenerative dissonance. He travelled to Karn to consult the Sisterhood and know if he could avoid his fate. He instead found out that the Doctor would repeatedly thwart his future attempts and be in his way. Determined to stop him before it happened, he tracked him down to Earth, but the Doctor tricked him and took away his TARDIS, before leaving him to UNIT.

Eventually, though, the Two managed to escape. He deceived Harry Sullivan, making him think he was the Doctor, into studying a piece of desentherium, a mineral who could open a time corridor. Unknown to him, the Doctor showed up, suffering from degeneration in his sixth body, and resolved the experiment for him and Harry, allowing the Two to travel back to 1963 and attempt to blow up the Doctor's TARDIS with a warp bomb, in order to destroy it, thus avoiding his future from happening. The Doctor, however, managed to reach his TARDIS and stop him in time by connecting himself to the TARDIS' telepathic circuits and confusing the Two into stupor. He then abandoned the Two on a desert planet, to give him a chance at redemption. (AUDIO: Two's Company)

Post-mortem
As the Eight began to regenerate, the Two told him that he tried his best but it was time for a 'better' man to take charge. He also told the Six to be quiet, telling him that none of them get to be in charge anymore, and to concentrate during the Eight's regeneration. (AUDIO: The Doomsday Chronometer)

The Two boasted that his "nose was particularly good at sniffing out traitors." Within the Eleven, he exposed Volstrom's betrayal of Padrac as an agent of Ollistra. (AUDIO: Songs of Love)

Personality
While on a mission for the High Council with the Twelve, the Eighth Doctor described the Two as "the charmer". (AUDIO: Planet of the Ogrons)

Behind the scenes

 * The script of Dark Universe describes the Two as "calm, reasonable, convincing, charming, liar and manipulator".