A is for... Azmael

An elderly Time Lord, described by the Doctor as one of his mentors. Azmael renounced the society of Time Lords to set himself up as the Master of Jaconda, a verdant world inhabited by bird-like people. Jaconda had been plagued by giant slug-like creatures - Gastropods - in its ancient history. It was believed that this was merely a myth, but a Gastropod egg had survived and it hatched out to produce Mestor. He quickly took over the planet and laid waste to it through a new generation of Gastropods. In order to expand his race, Mestor devised a plan to destroy the Jacondan solar system - the explosion spreading his near indestructible eggs across the galaxy. He fooled Azmael into thinking that he was acting in the planet's best interest - shifting neighbouring planets closer to the sun to create worlds where food could be grown. Azmael was sent to Earth to abduct a pair of twins who were mathematical prodigies. He did this, posing as an old friend of their father named Prof. Edgeworth.
The Sixth Doctor recognised him for who he really was, as he had visited Jaconda as recently as his fourth incarnation. On the last night of that visit, the two had gotten extremely drunk, and the Doctor had pushed Azmael into a fountain to sober up.
Azmael was horrified when the Doctor pointed out to him what Mestor was really trying to achieve. He sacrificed himself to absorb Mestor's life-force - holding it as he died, as he had reached the end of his final regeneration. The Doctor destroyed the Gastropod body, to prevent Mestor returning to it, and the old man died in his arms - recalling that last night by the fountain.

Appearances: The Twin Dilemma (1984). Played by Maurice Denham.

• There is a serious ethical concern raised in Azmael becoming the master of an alien world which is never addressed. Only the amoral Rani is known to have ruled another planet. Why does the Doctor not challenge him about ruling over another race - no matter how benignly - or the Time Lords for that matter? Surely this is the ultimate in interference in the affairs of another species. The Doctor then happily wanders off leaving a young human policeman in charge.
• Just why does Azmael need to use an alias when abducting the twins? There is no call for it unless he's somehow known on Earth, but nothing suggests this.