Borusa

Borusa was a notable and ultimately tragic figure in the history of the Time Lords of Gallifrey, and a very important figure in the life of the Doctor. At various points in his life, he assumed the ranks of Lord President, Cardinal and Chancellor of Gallifrey.

Early life and career
Borusa held the degree of a jurist and was a tutor to the First Doctor, (TV: The Deadly Assassin) the Master, (AUDIO: Masterplan) and the rest of the Deca at the Time Lord Academy. (PROSE: Divided Loyalties) Among the other subjects, he taught mind shielding. He wrote a paper on reason, which the Doctor had read. (TV: The Invasion of Time) As a junior Cardinal, he chaired the Committee of Enquiry into the activities of Morbius. (PROSE: Warmonger) Like the Doctor, Borusa was a member of the Prydonian Chapter.

His previous student, Magnus, began to rise rapidly in the Time Lord hierarchy, and Cardinal Borusa saw him as a threat to his own position of power, and persuaded the Celestial Intervention Agency to manufacture evidence of treason against him. Believed to be a criminal, Magnus fled from Gallifrey and became a renegade. (PROSE: Timewyrm: Exodus)

Involvement with the Master
When the Fourth Doctor returned to Gallifrey to defeat the Master, Borusa was Lord Cardinal on the High Council. He set about "adjusting the truth" in the wake of these events, portraying the late Chancellor Goth not as the Master's ally, but as a hero who had given his life to stop the Master. Unsurprisingly, the Doctor was appalled, and was more than happy to leave Gallifrey in return for the charges against him (of assassinating the President) being dropped. (TV: The Deadly Assassin)

During the Sontaran invasion
After the Doctor left Gallifrey again, Borusa officially became Lord Chancellor — apparently illegally — and at some point regenerated. The Doctor returned to Gallifrey briefly to officially take up the post of Lord President — which he had nominated for as a legal ploy during his previous trial, and which he automatically held after rival candidate Goth had died — as part of a strategy to defeat the Vardans. Once they and their puppet masters, the Sontarans, had been seen off, the Doctor departed, again leaving Gallifrey in Borusa's hands. (TV: The Invasion of Time)

Career as Lord President
Some time before the second crisis involving Omega, Borusa was inducted officially as Lord President, and regenerated again. Councillor Hedin left evidence of his own crimes that made it seem that Borusa was the criminal. Borusa corrected the Time Lords, revealing Hedin's wrongdoing, and hoped that Omega would find peace after the Fifth Doctor sent him back to the antimatter universe. (TV: Arc of Infinity)

Descending into madness
Regenerating yet again — with his stubborn streak apparently enhanced in the process — Borusa used his presidential powers to investigate the legacy of Rassilon from the Dark Time of Gallifrey. He pursued access to the Tomb of Rassilon, where he believed he would find the secret of immortality, ruling Gallifrey forever as "President Eternal". To this end, he reactivated the ancient Time Scoop, and revived the long-forbidden war games between captured representatives of various species in the Death Zone surrounding the Tomb.

Borusa summoned all of the Doctor's previous incarnations to the Zone (though the Fourth Doctor ended up becoming trapped in the Time Vortex), convinced that at least one would gain entry to the Tomb. Once three of them had, he tricked them into deactivating the forcefield blocking transmat access to the Tomb. After reaching the Tomb, however, he found that the promised immortality was a trap set by Rassilon to capture power-mongers such as himself. Borusa was condemned, like others before him, to live his "immortal" life trapped within a sarcophagus. (TV: The Five Doctors)

Revival and retirement
The Eighth Doctor persuaded Rassilon to free Borusa from his immortality to reform the corrupt High Council and to defend the Sixth Doctor at his trial. He was released from his punishment to carry out this duty- simultaneously being regressed back to an earlier, more stable incarnation- but apparently returned to Rassilon afterwards. (PROSE: The Eight Doctors) He was released once again when the Committee of Three — a group of renegade Time Lords whose careers had been ruined by the Doctor's actions — attempted to use the powerful Agonal against Rassilon to make him release Borusa, but, having seen the error of his ways, Borusa instead aided Rassilon, Romana and the Seventh Doctor in defeating Agonal before he passed on for good. (PROSE: Blood Harvest)

Last Great Time War
Another source showed Borusa alive during the Last Great Time War. Borusa had been retro-evolved by Rassilon to become a possibility engine. He resided in the Dark Tower in the Death Zone. Rassilon used Borusa to predict the most suitable timeline for Time Lord victory throughout the War. Rassilon came to Borusa to ask him about the most successful way to detonate the Tear of Isha into the Tantalus Eye.

The War Doctor later stole Borusa from Rassilon. Being further altered by proximity to the Tantalus Eye, Borusa helped the Doctor to erase all presence of the Daleks around the Tantalus Eye. He was killed in the process but that was the fate he wanted after a miserable existence as Rassilon's experiment. (PROSE: Engines of War)

Personality
Borusa seemed to have been a strict teacher towards the Doctor, and didn't give his former pupil much credit for saving Gallifrey from the Master (giving him a mark of nine out of ten). (TV: The Deadly Assassin) However, the pair seemed to have a love/hate relationship, only for their relationship to completely shatter when Borusa placed all of the Doctor's incarnations in mortal danger. (TV: The Five Doctors)

Behind the scenes

 * Borusa is one of the few Time Lords to be depicted in televised episodes through multiple regenerations on-screen.
 * According to The Brilliant Book 2012, Borusa's Portrait of Rassilon was stolen during his tenure as Lord President. The Corsair, a renegade Time Lord with whom the Doctor was friends, was accused of and censured for the crime.
 * In the TV sketch The Pitch of Fear, Mark Gatiss plays a character called Mr Borusa, obviously in reference to the character.

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