Adelphi

Adelphi of the Arcalian Chapter was a councillor on Pandad IV's High Council of the Time Lords, and a member of the tribunal that sentenced the War Lord and the Second Doctor during their own separate trials. He later came to Earth on several occasions to give the Third Doctor warnings, (PROSE: Doctor Who and the Terror of the Autons, The Legacy of Gallifrey) such as warning him of 's arrival on Earth. (TV: Terror of the Autons)

The Doctor's trial
Adelphi was a member of the High Council, in addition to serving on the tribunal that sentenced the Doctor. PROSE: Doctor Who and the Terror of the Autons) He had been sent to the tribunal on orders of Lord President Pandad IV as a direct result of Rassilon's agent, Socra, being asked by his Matrix Lord masters to keep an eye on the Doctor. (PROSE: The Legacy of Gallifrey)

Adelphi, along with the Time Lords Socra and Goth, captured the War Lord after being alerted to his plans by the Second Doctor's Hypercube. He personally explained what the War Lord and his people had done, and how his plans were "an utterly callous disregard for the lives of the humans involved, and for the liberties of all the other species in the galaxy." When he asked the War Lord if he had anything to say in his defence, the War Lord refused to say anything. Adelphi used some of his power to cause intense pain for the War Lord until he spoke, saying that the Doctor collaborated with the War Chief, and that the Doctor was guilty too for it. Adelphi sentenced the War Lord to dematerialisation, wiping him out of existence after his verdict of guilty was reached. Adelphi then listened to the Doctor's defence when his own trial came up and listened as the Doctor passionately addressed the Time Lords' own non-intervention policy and saying they should be helping those in need much like he did. Adelphi later witnessed the Doctor refuse every new appearance offered to him when he and Goth announced his punishment for breaking the Laws of Time was an exile on Earth and a forced regeneration. (TV: The War Games)

Serving as a messenger
Following a regeneration, Adelphi served as a messenger to the Third Doctor during his exile. (TV: Terror of the Autons) In this capacity, he first encountered the Doctor when he appeared in his TARDIS while the Doctor was with his companion Liz Shaw. (AUDIO: Shadow of the Past)

After the Doctor's defeat of Helios, Adelphi spoke to the wardens of Shada, requesting that they release to keep the Doctor busy on Earth. (PROSE: Prisoners of the Sun) He then travelled to Earth to warn the Doctor of the Master's arrival and of an impending trap that the Master had set for him. When the Doctor asked for assistance in dealing with the trap, however, Adelphi simply disappeared. (TV: Terror of the Autons)

He was sent to see the Doctor again in order to persuade him not to investigate the death of a future companion whom the Doctor had not yet taken on board the TARDIS, (PROSE: An Overture Too Early) and also told the Sixth Doctor about the many different versions of Peri Brown that were in the universe after the High Councils interfered with events of Thoros-Beta. (AUDIO: Peri and the Piscon Paradox)

The Doomsday Weapon crisis
When a report on the Doomsday Weapon went missing from the Time Lords' files, Adelphi, again having regenerated into another incarnation, was one of those convinced the Master had taken it while making a report to Pandad IV. Together, they, along with a third Time Lord, sent the Doctor and Jo Grant to the planet Uxarieus in the year 2472 to investigate. Adelphi expressed doubt over whether or not the Doctor would help, and he pointed out the Doctor had good reason to resent them since they had taken away his freedom, though he silently accepted that his freedom would be temporarily restored to investigate what the Master was doing. (TV: Colony in Space)

Behind the scenes

 * Adelphi first appeared in the 1969 serial The War Games as an unnamed Time Lord Councillor played by Trevor Martin, who was credited as "Time Lord 2". He appeared again in 1971's Terror of the Autons as a Time Lord messenger played by David Garth. Terrance Dicks' novelisation of Terror of the Autons revealed that the messenger had been part of the tribunal that sentenced the Doctor in The War Games. The character finally received a name in The Legacy of Gallifrey by Gary Russell, a 1985 short story in Doctor Who Magazine 100 that provided an in-universe history of Gallifrey and the Time Lords. The Legacy of Gallifrey named the three members of the tribunal as Goth, Socra and Adelphi. Because it explicitly established both Goth and Socra as separate from the Time Lord messenger, The Legacy of Gallifrey confirmed that Adelphi and the messenger were the same individual.
 * Some time after he played "Time Lord 2", Trevor Martin played another, much more illustrious Time Lord off-screen: the Doctor himself in a new incarnation, first debuted in the play Doctor Who and the Daleks in Seven Keys to Doomsday and reprised the role its audio drama adaptation. The play was first performed in a theatre venue called the Adelphi, hence the name given to Martin's earlier Doctor Who character by Gary Russell.