Time war

The last great Time War

The last great Time War was first alluded to in the first episode of the 2005 series, Rose. There, the Ninth Doctor explained to his latest companion, Rose Tyler, that the reason behind the Nestene Consciousness' invasion of Earth was because its food planets were destroyed in a war. Later in the episode, the Doctor stated that he fought in the war, but he was unable to save the Nestenes' planet.

In the following episode, The End of the World, set five billion years in the future, Jabe of the Forest of Cheem expressed amazement that the Doctor, a Time Lord, still existed, implying that the war had consequences up and down history. At the end of that episode, the Doctor confessed to Rose that the war had destroyed his home planet (presumably Gallifrey, though never named as such) and left him the only surviving Time Lord.

In the third episode, The Unquiet Dead, the Doctor encountered the ghostly Gelth, aliens from another dimension whose bodies had been destroyed by the war. The Gelth said that the war was unseen by "lower species" but devastating to the "higher" ones.

In Dalek, the sixth episode, it was revealed that the Time Lords' adversaries in the war were the Daleks. What actually started the war was not stated, but executive producer Russell T. Davies commented in an episode of the documentary series Doctor Who Confidential that the origins of the war dated back to the 1975 serial Genesis of the Daleks, where the Time Lords sent the Fourth Doctor into the past in an attempt to avert the Daleks' creation or affect their development to make them less aggressive.

Further details of the War are sketchy; in Doomsday, the Tenth Doctor mentions that he fought on the front lines and was present at the Fall of Arcadia. In any case, at the war's end, the Doctor was responsible for the destruction of the Dalek fleet, an action that also destroyed the Time Lords and Gallifrey. Although at least the single Dalek in Dalek had survived, the Doctor dismissed the possibility that other Time Lords may have survived as well, saying that he would have sensed it if they had.

The destruction of the Time Lords created a vacuum that may have left history itself more vulnerable to change. In The Unquiet Dead, the Doctor told Rose that time was in flux and history could change instantly — a more fluid definition to that which had been seen in earlier stories, which had implied that history was either immutable (The Aztecs) or capable of being changed only by very powerful beings (Remembrance of the Daleks).

The most dramatic demonstration of this was in Father's Day, when Rose created a paradox by crossing her own timestream to save her father's life just before his intended death in a traffic accident. This summoned the terrifying Reapers, who descended to sterilise the "wound" in time by devouring everything in sight. The Doctor stated that if the Time Lords had been still around, they could have prevented or repaired the paradox. The consequences of creating a paradox were also why the Doctor could not go back in time and save the Time Lords. Indeed, such actions may have directly contributed to their near-extinction: "They’re all gone," the Ninth Doctor laments, "And now I’m going the same way."

Although the Doctor believed himself to be the last survivor of the Time War, in The Parting of the Ways he discovered that, in addition to the lone Dalek in Dalek, the Dalek Emperor itself had also survived, and had built a new Dalek race. Whether this means that other Time Lords may have survived as well is unclear. The apparent destruction of the Emperor and his fleet at the conclusion of the 2005 series by a time vortex-augmented Rose Tyler was accompanied by her declaration that "the Time War ends."

In the 2006 series episode School Reunion, while being tempted by the power of the Skasis Paradigm which would give him the ability to reorder the universe, the Doctor mused that he could "stop the war". In Rise of the Cybermen, the Doctor noted that when the Time Lords were around, travel between parallel universes was less difficult, but with their demise, the paths between worlds were closed. In The Satan Pit, the Beast says that he recognises the Doctor as "the killer of his own kind".

In Doomsday, it was revealed that a group of Daleks from the elite Cult of Skaro fled into the Void between dimensions and survived the original end of the Time War, taking with them the Genesis Ark, a Time Lord prison ship containing millions of Daleks. The new Dalek army released from the Ark was eventually sucked back into the Void due to the actions of the Doctor, but the black Dalek named Sec managed an "emergency temporal shift" and escaped.