Ryoth was a member of the High Council of the Time Lords. He was a member of the Arcalian Chapter and the Celestial Intervention Agency, who had suspected ties to Goth and Borusa. Despite these, he was allowed to continue in his current position, but only because he was too relatively minor for anyone to seriously worry about him.
When the Eighth Doctor was visiting his past selves, Ryoth attempted to turn public sentiment against President Flavia by revealing her lack of interest in punishing the Doctor for his disregard of the laws of Time, attempting to imply that her judgment was being clouded by her affection for the Doctor, but Flavia was able to end such claims by having her staff confirm that the Doctor's visits had so far posed no danger to Gallifrey or the Web of Time and action would be taken if they were a threat.
Having convinced the Agency of the potential threat posed by the Doctor, Ryoth attempted to kill the Eighth Doctor during his visit to his fifth incarnation by using the Time Scoop, the Agency permitting him to take action as a deniable agent. However, the Doctors were able to deactivate the Raston Warrior Robot he sent after them before turning it on the Sontaran battle group Ryoth sent when that failed. When he tried to unleash a Drashig on them, the Doctors were able to set up a Temporal Reverse Feedback Field that sent the Drashig to Ryoth instead. He was killed instantly and the Time Scoop destroyed. (PROSE: The Eight Doctors)