The Miaxa was a peaceful leader who led the Blightstar Hegemony until he went mad.
The Miaxa founded the Blightstar Hegemony, a peaceful alliance of thousands of worlds. At some point, he developed a split personality and started a war within the Hegemony. Eventually, one part of the personality was able to subdue the other and stop the war. Fearing that he would start another war, the Miaxa decided to isolate himself at the edge of the known universe. The Miaxa was from a species of powerful psychics and the split personalities were able to create physical forms. The Miaxa created a prison to hold these personalities, but the insane personality took control. Calling itself "the Warden", it tortured "the Prisoner" personality for thousands of years, killing it over and over again. The psychic powers allowed the Prisoner to reconstitute itself, only to die yet again. Over time, both forgot why they were there and both thought the other was the insane Miaxa.
When the Fifth Doctor and Nyssa came to the asteroid where the prison was, they encountered the Prisoner first. The Doctor broke into his cell to try to free him, while Nyssa went in search of help. She was captured and forced into a compliance collar by the Warden, who thought she was an accomplice of the Prisoner. The emergency execution protocol was activated on the force field, set to kill the Doctor and the Prisoner in 4 minutes. When the Doctor revealed the true history to the Warden and the Prisoner, the Warden decided to save the Doctor but still refused to rescue the Prisoner. During the escape attempt, the Warden was trapped in the cell. Both were killed, but their psychic powers allowed them to reconstitute themselves as a single mind again. They both thought they were still too dangerous to be released again. The Doctor agreed to set up a device to free them when their aggression had been managed, but actually just set up a timer to release them in three months. He believed that they would become peaceful if they believed they were peaceful. (AUDIO: 1001 Nights)