would die on that day, Rassilon refuses to accept his fate and killed his advisor for speaking out against his plans. Anticipating Gallifrey's complete annihilation in "The End of Time" (2009–10), Rassilon attempted to break the planet out of the Time Lock implemented in the latter phases of the Time War to block creative attacks involving time travel, placing a drumbeat (actually the heartbeat of Gallifreyian twin-hearts) in the mind of the Master when he was a child. As a result, Rassilon is the cause of the Master's insanity and indirectly responsible for the Time Lord's actions. When the Master turned all of humanity into copies of himself, the now-amplified drum beat acts as a signal that, with a White Point Star diamond (a diamond unique to the planet, Gallifrey), allows Rassilon and Gallifrey to escape the Time Lock. Destroying the White Point Star, the Doctor severs the link between Gallifrey and Earth. Rassilon's attempts to kill the Doctor in revenge are blocked by the Master, vengeful owing to his manipulation by Rassilon, who then follows him and the other Time Lords into the last day of the Time War. In "The Day of the Doctor" (2013), the Time Lords are revealed not to have been destroyed at the Time War's conclusion; all incarnations of the Doctor united and used their TARDISes to send Gallifrey into a pocket dimension. In "Hell Bent" (2015), the Twelfth Doctor arrives on Gallifrey and learns that a regenerated Rassilon was responsible for his imprisonment and torture for four and a half billion years, as well as indirectly responsible for the death of his companion, Clara. On arriving on Gallifrey, he leads a military revolt against Rassilon, deposes him, and sends him into exile. Timothy Dalton was asked to reprise the role for the episode, but was replaced by Donald Sumpter as a regenerated Rassilon when he became unavailable for filming. Other appearances Rassilon's rise to power was explored in the Virgin New Adventures novel Cat's Cradle: Time's Crucible. It is revealed in the novel that Ancient Gallifrey was ruled by the Pythia, who controlled the population through prophecies and superstition. Rassilon, whose followers believed in science and rationality, led a revolution against the Pythia, eventually causing her to kill herself, and send her followers to the planet Karn. However, before she died she cursed Rassilon and all future Time Lords to sterility. Rassilon's unborn