Tegorak

Tegorak, whose name meant Black Mountain, (NC: Alternative Chronologies) was was an individual from Gallifreyan history who was obscure by the Infinity Doctor's era. (PROSE: The Infinity Doctors)

Tegorak was a Lord Cardinal of the Arcalian Chapter who became the youngest ever President of the High Council when the prior President was killed in a Sybaril invasion of Gallifrey around 150,000 years after Rassilon created the Time Lords. Wearing symbolic armour, Tegorak defeated the Sybaril invasion himself, then announced an invasion of Kasterborous to establish a protective line of defence around Gallifrey and prevent further invasions. He left Gallifrey to lead the invasion, appointing his friend, High Chancellor Garlan, to rule in his absence. However, the Matrix Lords convinced Garlan that Tegorak's mercenary followers would create an empire and supplant Time Lord society, and Garlan turned against Tegorak: first, he sent an assassin to kill him; then, when Tegorak returned to discuss the assassination attempt, he was shot down in the Panopticon. Although Tegorak used the Presidential Time Ring to escape to his TARDIS to regenerate, Rassilon laid a trap for Tegorak and prevented him from taking any revenge on Gallifrey. (NC: Alternative Chronologies)

A vast suit of armour which once belonged to Tegorak was among the artefacts in Archive Chamber 403, with a rusty plaque explaining its history. Captain Raimor didn't recognise the name "Tegorak". (PROSE: The Infinity Doctors)

Behind the scenes
Tegorak and his story were detailed in the second issue of Adrian Middleton's fanzine Apocrypha, originating from Middleton's unpublished fanfiction Black Mountain. Middleton intended Tegorak to be a Gallifreyan version of Julius Caesar or King Arthur, "an allegorical character who did nothing but good for his people, and who was repaid with betrayal by his closest friends."