Niroc was Lord President of the Time Lords after the Doctor was deposed during his long absence. The Celestial Intervention Agency removed Acting President Flavia from office and instated Niroc, a much more controllable President, in her place.
It was believed that Niroc oversaw or took part in Operation Ravolox and had purposefully put the Doctor on trial to prevent the truth from coming out. His High Council enlisted the Valeyard, a future manifestation of the Doctor's evil side, to act as prosecuting attorney and present fake evidence at the trial. In return, the Valeyard would receive the Doctor's remaining regenerations. (TV: The Trial of a Time Lord, PROSE: TheEight Doctors)
At the end of Niroc's presidency, the details of the Ravalox incident were revealed in a presidential inquiry arranged by the Sixth and Eighth Doctors — invoking their rights as ex-President and the fact that the Sixth Doctor's dismissal from the role in absentia made it of questionable legality — and Gallifrey faced threats of disunity, as well as a potential Shobogan uprising. While the Sixth Doctor dealt with the Valeyard, the Eighth Doctor asked Rassilon to free Borusa from his imprisonment and lead Gallifrey out of this difficult period. Flavia noted that most of the renegade High Council from this time would soon be put on trial themselves to determine who were genuinely guilty and who were merely fools. (PROSE: The Eight Doctors)