During the Last Great Time War, Rassilon was resurrected from the Matrix by Project Revenant to lead the Time Lords against the Daleks, becoming Rassilon the Resurrected, though he was forced to regenerate after only a short time when he was attacked by the Sicari, an attack that had been orchestrated by Romana II.
Following his final death, (PROSE: Pandoric's Box) Rassilon was able to survive by copying his mind into the Matrix, (AUDIO: Zagreus) where he continued to manipulate Gallifrey with the Matrix Lords (PROSE: The Legacy of Gallifrey) until he was cast into the Divergent Universe by the Eighth Doctor. (AUDIO: Zagreus) Rassilon's mind eventually broke free from the Divergent Universe and was reincorporated with his Matrix projection, (Desperate Measures) allowing him to be resurrected from his tomb in the Dark Tower within the Death Zone to lead the Time Lords to battle during the early days of the Time War. (PROSE: Engines of War) To resurrect him, the High Council used the body of Admiral Valerian of the House of Rassilon and imprinted Rassilon's Matrix projection onto him, killing Valerian in the process. (AUDIO: Desperate Measures)
Rassilon's early actions involved replacing the office of High Chancellor with a Prime Minister (appointing the War Livia Caralis to the role), dissolving the Chancellery Guard and using the Drylands Precedent to create an Interior Defence Unit in its place without the need of the support of the Joint Council. He appointed Cardinal Mantus to lead the IDU. He also pardoned Romana II from charges of treason for secretly negotiating with the Dalek Emperor and reinstated her as Coordinator of the Celestial Intervention Agency. After General Trave's future self arrived on Gallifrey to warn the past of Rassilon's regime leading to Gallifrey's downfall, Rassilon charged the contemporous Trave with his future self's crimes and had him publicly executed. (AUDIO: Havoc)
Having lost many of his disdains for corruption and immortality with his resurrection, (PROSE: A Brief History of Time Lords) Rassilon wiped out the Tharils, the Porfue and the Krajonnu in the first year of the Time War so that they didn't threaten the Time Lord's supremacy. (PROSE: Lords and Masters)
Rassilon arranged the breaching of the time freeze around Ysalus to force the War Council to destroy the planet as an example. (AUDIO: Collateral) After discovering this, Romana schemed with Livia to assassinate him, allowing the Sicari to breach Gallifrey's defences and manipulating events to get Rassilon alone. At the same time, Rassilon attempted to win round her deputy, Narvin, meeting him to praise his past decision to send the Fourth Doctor to try to avert the creation of the Daleks. The Sicari did manage to wound Rassilon, forcing him to the brink of regeneration, but his guards reached him in time to save him. To Romana's shock he actually delighted in her and Livia's actions, happy this generation of Time Lords were as cunning as his had been, and welcomed Livia back into fold. He ordered Mantus to exile Romana and Narvin and shut down the Celestial Intervention Agency, absorbing it into the IDU. His regeneration was broadcast across Gallifrey, increasing his influence over the Time Lords. (AUDIO: Assassins)