Mantus was a member of the War Council during the Last Great Time War.
He was in charge of the inquiry of treason against Romana II. He worked closely with Rassilon. He became head of the Interior Defence Unit. He was also an advisor and private secretary to Rassilon. He had Bovari arrested for supplying the Celestial Intervention Agency with the evidence they needed. He later ordered the execution of Trave and threatened his family if he spoke out. (AUDIO: Havoc)
He got wind of Romana's plan on Ysalus and asked Aladra to find out what the Celestial Intervention Agency was doing there. He wanted to make an intervention to destroy Ysalus to set up a front in the war. (AUDIO: Partisans)
He chastised Romana for her evacuation of Ysalus. He accidentally revealed that the breach of Ysalus' time freeze was ordered by Rassilon. He had Dalia erased from time. He then told Narvin about Rassilon's request for the CIA. (AUDIO: Collateral)
He offered Narvin a new regeneration cycle, (AUDIO: Assassins) as he was no longer able to regenerate after his ordeal on an alternative Gallifrey. (AUDIO: Reborn)