Twelfth Doctor (The Curse of Fatal Death)

The Twelfth Doctor came into being when his previous incarnation regenerated after an electrical mishap. As he said: "Now look at that, I've gone and wasted three whole bodies in just under a minute and all because I forgot to unplug."

He proved the shortest-lived, only living long enough to shut off a zectronic energy generator before being hit by excess zectronic energy, subsequently dying due to the exposure; allegedly, zectronic energy would kill Time Lords beyond any hope of regeneration. He gave a final speech to Emma and the Master, asking them to "look after the universe for me - I've put a lot of work into it" and promised to explain later before dying, 'I'll... explain..." His foes the Daleks and the Master vowed to reform and live better lives because of him, but then, unexpectedly, he regenerated into a new incarnation. (DW: The Curse of Fatal Death)

Behind the scenes

 * The line "I've put a lot of work into it" would later be incorporated into The Eleventh Hour (also written by Moffat), spoken by the true Eleventh Doctor, referring to Earth while responding to the Atraxi's comment that he was not a native of the planet.