Following the Last Great Time War, Rassilon, in an incarnation who dubbed himself Rassilon the Redeemer, guided his people to returning Gallifrey to the universe from the pocket universe where it had been sent to by the Doctor. However, after ordering him placed in a confession dial in an effort to find out the truth about the Hybrid, Rassilon was deposed by the Twelfth Doctor and exiled from Gallifrey.
On the final day of the Last Great Time War, Rassilon planned to initiate the Ultimate Sanction with his High Council, breaking the time lock to free Gallifrey and unraveling the Time Vortex itself in order to destroy creation and leave the physical universe, only to be foiled by the Tenth Doctor and the Master, the latter of whom attacked Rassilon to force him back onto Gallifrey, (TV: The End of Time) just as the thirteen Doctors sealed it away in a pocket dimension with a Stasis cube. (TV: The Day of the Doctor) Rassilon's battle with the Master caused him to regenerate, (PROSE: Pandoric's Box) reportedly because the Master "shoved White Point Stars down his throat". Rassilon screamed all the way through the regeneration, so much that Ohila had to make him "a special draft of potion" to help. (PROSE: Lords and Masters) Despite Rassilon's previous intention to kill the "diseased" Master, (TV: The End of Time) the Time Lords instead cured the Master's "condition" (TV: The Doctor Falls) and locked him up in Gomer's Asylum, which he later escaped from. (PROSE: Lords and Masters)
Siege of Trenzalore
After the Doctors united to place Gallifrey in a stasis cube to prevent its destruction, (TV: The Day of the Doctor) Rassilon began work to place it back in the main universe. When the Matrix detected a tear in the fabric of a nearby reality, Rassilon, keen to avoid another Time War, broadcasted a signal from the planet Trenzalore, calling to the Eleventh Doctor to see if it was safe to return. When the signal led to the Siege of Trenzalore, Rassilon continued to wait for the Doctor's signal until Clara Oswald alerted him and the Time Lords to the Doctor's inability to regenerate and that the Daleks were preparing to kill him. (PROSE: A Brief History of Time Lords) Using research gathered from Ophiuchus's experience with regeneration, (COMIC: Ophiuchus) Rassilon granted the Doctor a new regeneration cycle, but the Doctor left Trenzalore without freeing Gallifrey. Nonetheless, Rassilon had confirmed that he'd found the right universe and was quick to return Gallifrey to it. (PROSE: A Brief History of Time Lords)
Return to N-Space
The Time Lords later returned Gallifrey to its original point in space but were forced to hide it near the end of the universe for their own safety. (TV: Hell Bent) At some point afterwards, Rassilon was taken to the Death Zone by Pandoric to offer advice to his former self in whether to use the Galaxy Eater to destroy the Nestenes. He told his former self that Gallifrey would stand past all its conflicts. (PROSE: Pandoric's Box)
Rassilon took members of the House of Stillhaven to be experimented on, but he spared Yayani to a mind wipe for unknown reasons. After Yayani was able to regain her memories, she tried to assassinate Rassilon, but failed, and was then forced into acting out secret missions for the High Council as punishment. (PROSE: Lords and Masters)
Banished from Gallifrey
Still fearing the Visionary's prophecy, Rassilon began to fear that the fall she had foreseen would be brought about by the Hybrid and began researching the creature. Possibly due to being influenced by Missy, Rassilon came to believe that the Twelfth Doctor held the information he desired. Ordering the death of Clara Oswald, Rassilon trapped the Doctor in his confession dial to get information out of him. (PROSE: A Brief History of Time Lords) To this end, Rassilon contacted Ashildr to have her assistance in the kidnapping of the Doctor, (TV: Face the Raven, Hell Bent) and trap him within his own confession dial in an attempt to learn everything that he knew about the Hybrid. The Doctor's refusal to relent led to his being trapped inside the dial for four and a half billion years, constantly dying and recreating himself to breach the dial's barriers rather than confess his secrets. (TV: Heaven Sent, Hell Bent) On his escape, the Doctor finally returned to Gallifrey. (TV: Heaven Sent)
Threatened by the Doctor's presence, and still desperate for information on the Hybrid, Rassilon ordered first troops and then the High Council to make contact with the Doctor. However, the Doctor was only willing to speak directly to Rassilon himself. Eventually, Rassilon was forced out into the Drylands to confront him, where the Doctor held him alone responsible for the crimes of the Last Great Time War, and for his treatment in his confession dial. Rassilon tried to have a firing squad execute the Doctor, who ordered him to "get off [his] planet." However, the squad purposefully missed due to their great respect for the Doctor. Military reinforcements arrived but had been summoned by the Doctor instead. When Rassilon tried to use his gauntlet to kill the Doctor himself, the Eleventh General reinforced the Doctor's order. Rassilon was overthrown and replaced by the Doctor, before being banished from Gallifrey. (TV: Hell Bent)
Alliance with the Cybermen
Barely concerned by his exile, Rassilon eventually found the remnants of the Cybermen, who were clinging to life at the end of the universe. Marvelling at their sense of purpose in a dead universe, Rassilon convinced them to ally with him, promising them a new empire built on a Time Lord/Cyberman union, and was upgraded into the Cyberiad as the Cyber-President. Leading the Gallifreyan Cyber Fleet back to his home planet, Rassilon granted the Cybermen the ability to conquer all of time and space, and together, they overran the Time Lord militia, with Rassilon personally executing his successor as he reclaimed his gauntlet.
To Rassilon's dismay however, the near-death state of the universe did not lend itself to conquest. Conspiring to start again, Rassilon ordered the capture of several Time Lords, wiring them into Looms to harvest their regeneration energy into the Eye of Harmony, through which he would mould a new reality in his own likeness and be "a god, worshipped by all". Needing to throw the Doctor off the trail, Rassilon created several scenarios throughout history to distract him from the true plan.
Despite Rassilon's best efforts, the Twelfth Doctor managed to return to Gallifrey, where he confronted the Cyber-President. Once the Doctor and the Twelfth General had been taken prisoner, Rassilon wired the latter into a Loom before he explained his plan to the Doctor. It was then, just as the Doctor predicted, that the Cybermen betrayed Rassilon, intending to rewrite reality to their design.
Forced inside a Loom, Rassilon realised his mistakes and follies. Feigning unconsciousness, Rassilon created a simulation of the Doctor's boyhood barn within the Cyberiad so he could speak to his fellow Time Lord privately. When, as Rassilon predicted, the Cybermen plugged the Doctor in as a substitute for him, Rassilon greeted him and finally conceded that the Doctor was the better man, humbly asking for his help. When both their physical forms were fully upgraded, the two used their mental powers to sabotage the Eye of Harmony and send all the regeneration energy harvested by the Cybermen backwards through time, undoing the Cybermen's changes to history.
Following the erasure of the timeline, Rassilon was once again left in his Bowship at the end of the universe. Reflecting on these events, the Twelfth Doctor wondered if Rassilon had retained his memory of the timeline's events, but expressed the belief that Rassilon deserved to remember. (COMIC: Supremacy of the Cybermen)