The Eleven was an infamous Time Lord criminal. He went insane after his personality fractured into a torrential conglomeration of his past and present incarnations constantly fighting and arguing with each other in his head for dominant control. Following this, he would continue accumulating more personalities as he regenerated, giving rise to his current epithet in his eleventh incarnation.
Biography
In his first incarnation, the One worked in the Panopticon Archive, where he found information about a prototype of a stellar manipulator. (AUDIO: The Satanic Mill) He also had a seat on the High Council.
At some point, the Eleven developed personality defects which allowed his other incarnations to live on inside his mind. The Eleven turned to criminal activity after this.
In his eighth incarnation, the Eight decided to try to be a good man. Using meditation, he was able to suppress the voices of his previous incarnations. He attempted to stop the Eighth Doctor from assembling the Doomsday Chronometer. After he was killed by The Clocksmith, the Eight retreated into the Doctor's TARDIS and regenerated.
The Nine decided to return to the criminal ways of his previous incarnations. He convinced
The Eleven was captured by the Seventh Doctor and imprisoned on Gallifrey.
When he escaped, he managed to steal a TARDIS. The Eighth Doctor was brought in to find him. He installed himself as President by an ancient edict as he created a state of emergency and the President was off-world. He used the Sash of Rassilon to freeze the Time Lords. (AUDIO: The Eleven)
The Eleven hired Fortuna and Cleaver to bring the Doctor to him. (AUDIO: The Galileo Trap)
The Eleven found the prototype stellar manipulator and planned to use the death of a Time Lord to activate it and destroy the Sol system. He captured the Doctor for these means. The Eleven's plans were prevented by an unknown force, and the Doctor's screwdriver signalled for the TARDIS to land near the Doctor, allowing him to escape. (AUDIO: The Satanic Mill)
He was once interviewed by Caleera for the archives, as he knew she was special. He convinced her to amplify her powers for his plans. (AUDIO: Scenes From Her Life) He then came to Syra as part of his plans with Caleera. He planned a trap in the mines to kill The Doctor. He tried to kill Liv in the mines until River Song stopped him. He wanted to use Caleera to destroy planets. (AUDIO: The Sonomancer)