Twelfth Doctor (The Curse of Fatal Death)

The Twelfth Doctor was the result of the regeneration of the Eleventh Doctor.

Biography
The Twelfth Doctor came into being when his previous incarnation regenerated after an electrical mishap. He noted that he had wasted three incarnations in a very short time span simply because he "forgot to unplug". He proved the shortest-lived incarnation, only living long enough to shut off a zectronic energy generator before being hit by excess zectronic energy. He immediately died from the exposure as, allegedly, zectronic energy would kill Time Lords beyond any hope of regeneration.

He gave a final speech to Emma and, asking them to "look after the universe" for him, as he had "put a lot of work into it", and then died. His foes, the Daleks and the Master, vowed to reform and live better lives because of his sacrifice.

Unexpectedly, he regenerated into a female incarnation. (TV: The Curse of Fatal Death)

Sometime later his final words, "look after the universe for me, I've put a lot of work into it", would be uttered by another Twelfth Doctor, on Karn, when that incarnation believed he would die. (WC: Prologue)

Behind the scenes

 * In an early draft of the script, this incarnation was referred to as "The Gorgeous Doctor", with a parenthetical suggestion that he be played by Robson Green. His final name, used in the behind-the-scenes documentary and in Doctor Who Magazine credits, was "The Handsome Doctor".
 * Russell T Davies later offered the role of the Ninth Doctor to Hugh Grant, who declined, thinking the show would not be a success, a decision he later came to regret.
 * The line, "I've put a lot of work into it", would later be incorporated into the television story The Eleventh Hour, also written by Moffat, spoken by Matt Smith's Eleventh Doctor, referring to Earth while responding to the Atraxi's comment that he was not a native of the planet. The full line was also stated by Peter Capaldi's Twelfth Doctor to the Sisterhood of Karn in the Series 9 prelude webcast Prologue when he believed his latest adventure would result in his end.