New Doctor (Full Fathom Five)

Regenerating after his previous incarnation was killed, an incarnation of the Doctor from a parallel universe awoke. Disorientated and confused he said just a few words: "Hello, I'm the Doctor. Who are you?" Ruth Mills introduced herself and then coldly added, "Goodbye" before she shot him dead, triggering another regeneration while Ruth coldly mused how many more lives he had left to go before he died. (AUDIO: Full Fathom Five)

Behind the scenes
Ian Brooker's single line as this alternative Doctor has earned him the record for shortest recorded performance as the Doctor.