Azmael

According to the Scrolls of Gallifrey, Azmeal was Rassilon's confidant, the first High Chancellor of Gallifrey, and the first true Renegade of the Time Lord society Rassilon had founded.

The first Chancellor
After Rassilon's abdication from the Presidency of the Time Lords, the government was restructured on a more stable basis; Cardinal Pandad became the new Lord President, with a Chancellor immediately below him, a Castellan, the Prydonian Cardinals, and four Councillors. The post of Chancellor went to Azmeal, whom the increasingly secretive Rassilon took into his confidence about the position of the Great Key to the Eye of Harmony, also decreeing that to make sure no Time Lord would ever both be in charge of Gallifrey's government and in power over the Eye, Azmeal could never be allowed to ascend to the rank of President, nor any other Chancellor after him. (PROSE: The Legacy of Gallifrey)

Rassilon's apprentice
Azmeal gained Rassilon's trust to such an extent that when the Founder discovered the twelve-regeneration limit when fruitlessly attempting his thirteenth regeneration, it was Azmeal whose help he enlisted to help with his last shot at immortality: Azmeal worked the machines as Rassilon's mind was the first full Gallifreyan intelligence to be uploaded into the Matrix. (PROSE: The Legacy of Gallifrey)

Loss of his position
Following the Civil War between Pandad's Gallifrey and the rival presidency of Morbius, it was decreed that the Lord President and High Chancellor would, from now on, belong to the same Chapter, ensuring minimal friction. As the new President following Pandad's death, Helron, was Arcalian, this effectively put Azmeal "out of a job". (PROSE: The Legacy of Gallifrey)

A hounded scholar
Azmeal was not too displeased to lose his political position, as it freed his schedule to study the secrets of the Matrix which his master Rassilon had just barely begun to show him upon his death. As he studied further and further, Azmeal progressively discovered hints that the minds of the dead Time Lords were not static records of memories, but rather active as disembodied intelligences still guiding things from the shadows with Rassilon as their leader. Azmeal's growing influence over the Matrix, which they still did not understand themselves, led to Helron and his government planning to remove Helron from Gallifrey in his final incarnation, in forced retirement, as a way to stop him fro studying it further. (PROSE: The Legacy of Gallifrey) This was an offer which Professor Chronotis was the only Time Lord ever to actually accept. (PROSE: Shada)

The Renegade
Azmeal fled Gallifrey and Helron's goons, and continued his experiments on an alien planet. However, he was soon found by a warrior race in Helron's employ who destroyed the planet and all its inhabitants to bring Azmeal back to Gallifrey to stand trial. Upon returning, Azmeal formally became the first Renegade Time Lord, slaughtering the treacherous Helron and his High Council. The next High Council cautiously allowed him to make an escape and continue his experiments elsewhere. (PROSE: The Legacy of Gallifrey)

Legacy
Azmeal was the first of many Renegade Time Lords to formally renounce the values and laws of Gallifrey: he was an inspiration to a whole generation of young Time Lords at the Academy, including the Doctor, the Master and the Rani, who deemed that Rassilon had been right to pronounce Time Lord society decadent upon his deathbed, and that a change must be undergone. In turn, each of the three left Gallifrey, (PROSE: The Legacy of Gallifrey) as did others of their classmates, such as Drax and the Monk. (PROSE: Divided Loyalties)

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 in The Twin Dilemma. At first glance, 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. However, this account does match serendipitously with the destruction of Azmael's first adopted world, Vitrol Minor, by the High Council from the novelisation of The Twin Dilemma, released a year later.

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.