Azmael

Azmael was a renegade Time Lord who emigrated from Gallifrey to the planet Jaconda, where he ruled compassionately until Mestor deposed him.

Early life
Like all Time Lords, Azmael was taken from his family at the age of eight for the selection process in the Drylands. Staring into the Untempered Schism as part of a Time Lord initiation rite, Azmael reacted by running away from what he saw in the Schism. (PROSE: A Brief History of Time Lords)

Azmael was a tutor for the First Doctor at the Prydonian Academy. The Sixth Doctor considered him as the best one he ever had. (TV: The Twin Dilemma) They both held a great respect for one another. Azmael was present when the Doctor was expelled from the Academy. He was Coordinator at this time. (PROSE: Divided Loyalties)

At some point during the Doctor's fourth incarnation, the Doctor and Azmael had an encounter in which Azmael drank so much the Doctor had to throw him into a fountain to sober him up. (TV: The Twin Dilemma)

Thirteenth Azmael
When the villainous Mestor, who commanded the Gastropods, came to power on Jaconda, he used a telepathic link with Azmael to dominate his mind. Mestor forced Azmael, who used the name Professor Edgeworth, to kidnap the two young genius identical twins Romulus and Remus Sylvest. By this time, Azmael had reached the end of his regeneration cycle.

Recently regenerated himself, the Sixth Doctor and Peri came to Titan III. There they saw the wreckage of a ship and rescued Lieutenant Hugo Lang. While exploring some tunnels on the asteroid, Peri and the Doctor were captured and taken to meet Azmael. The Doctor recognised Azmael as a friend from their homeworld of Gallifrey. Co-operating with Mestor to save his people, Azmael abandoned the Doctor and Peri, letting them be taken captive. However, when the Doctor and Peri were able to follow him to Jaconda. After being attacked by the Doctor due to post regeneration trauma, Azmael sided with the Doctor when his observations revealed Mestor's true plan to trigger a solar eruption that would destroy Jaconda and send Mestor's eggs out across the universe. When Mestor took possession of Azmael's body and the Doctor destroyed Mestor's real body, Azmael, with Mestor's consciousness within him, forced himself to die by attempting to regenerate. Since Azmael had already used all twelve of his regenerations, initiating a thirteenth regeneration resulted in both his and Mestor's deaths, which Mestor was unprepared for. (TV: The Twin Dilemma)

Behind the scenes
Inasmuch as it involves a Time Lord from the generation before the Doctor's who, in his 13th incarnation, flees from Gallifrey and takes refuge on a planet for which they come to care greatly, Azmeal's story in 1985's The Legacy of Gallifrey was highly reminiscent of the similarly-named Azmael, who had made his debut the year before. However, the two characters' histories do not actually match, with one of the bigger discrepancies being that Azmeal's adopted planet was destroyed by the Time Lords before he properly turned Renegade, whereas Azmael ruled Jaconda as a renegade.

Considering that the better part of The Legacy of Gallifrey is supposedly a translation of the writings of "Postar the Perfidious", supposing Postar to be an unreliable narrator who might have twisted Azmael's story into the tale of Azmeal is not too far-fetched an interpretation of the text, especially considering the conspicuous lack of any references to the actual Azmael even though Gary Russell otherwise took pains to reference every Time Lord story to date in The Legacy of Gallifrey. However, no in-universe sources have ever drawn such a link.