The Doctor's death

Much like their origin, the Doctor's death was a matter of conflicting accounts and alternate timelines. (PROSE: Alien Bodies, TV: The Impossible Astronaut, The Name of the Doctor)

Through their ability to regenerate, the Doctor was able to "cheat death" on numerous occasions. (TV: The Tenth Planet, The Parting of the Ways) However, the Tenth Doctor noted that he could be killed without allowing for regeneration. (TV: The End of Time) As such, the Doctor was not truly immortal, which the Fifth Doctor deemed impossible even for a Time Lord. (TV: The Five Doctors) Even allowing for regeneration, the Tenth Doctor regarded the change it entailed as a form of death. (TV: The End of Time)

Due to their impact on the universe, having "touched so many lives" and "saved so many people", the prospect of the Doctor's death would affect a great many people. Indeed, in one alternate timeline, news that the Doctor was dying led millions to offer their help. (TV: The Wedding of River Song) At the same time, Vislor Turlough, companion to the Fifth Doctor noted that the Doctor had many enemies who would delight in his death, an observation which Kamelion concurred with. (TV: The Caves of Androzani) Even once remarked that "a cosmos without the Doctor scarcely bears thinking about." (TV: The Five Doctors) Multiple occasions in which the Doctor was killed prematurely resulted in stars burning out across the universe. (AUDIO: The Furies, TV: Turn Left, The Name of the Doctor)

The Eighth Doctor was unique amongst his other incarnations in that he was technically dead both when he regenerated from the Seventh Doctor and when he regenerated into his successor incarnation. Following a non-fatal shooting, the Seventh Doctor was taken to a San Francisco hospital, where subsequent exploratory surgery by Grace Holloway with a camera accidentally clogged a vein; the anaesthetic he had been given delayed regeneration for several hours and almost destroyed the process. (TV: Doctor Who) The Eighth Doctor himself died aboard Cass Fermazzi's gunship when it crash-landed on Karn, but was resurrected for four minutes by the Sisterhood of Karn, enabling him to regenerate into the War Doctor. (TV: The Night of the Doctor)

Before encountering the Tenth Doctor, Sarah Jane Smith believed that the Doctor had died, having left her for so long without returning. (TV: School Reunion)

Lake Silencio
It was a matter of historical record that the Eleventh Doctor was killed at Lake Silencio, Utah on the planet Earth at 5:02 PM on 22 April 2011 at the hands of River Song, born Melody Pond. Knowing this, the crew of the Teselecta, a ship of the Justice Department which operated to inflict "hell" on unpunished criminals, deviated from their mission to punish Adolf Hitler when they discovered River. It was through this encounter that a younger version of the Eleventh Doctor became aware of his recorded death. (TV: Let's Kill Hitler)

Alternate timelines
In a confrontation with the Eleventh Doctor and Clara Oswald, the Great Intelligence entered the Doctor's time stream which he used to attack his entire timeline, turning all his victories into defeats. As a result, the Doctor was, as Vastra put it, "dying all at once", including on Androzani and in the Dalek Asylum. These deaths were averted when Clara went into the time stream, splintering herself into echoes whom saved the Doctor. (TV: The Name of the Doctor)