The Three Doctors (Doctor Who) the Third Doctor (Jon Pertwee) for help when Omega drains their civilisation's power. The serial opened the tenth anniversary year of the series, and features the first three Doctors all appearing in the same serial. This makes it the first "Doctor Who" story in which an earlier incarnation of the Doctor returns to the show. A superluminal signal is sent to Earth, carrying with it an energy blob that seems intent on capturing the Doctor. The homeworld of the Time Lords is also under siege, their power being drained through a black hole. Trapped themselves, and desperate to send help,
The Doctor (Doctor Who) "definite sense of Englishness". When Hartnell left the programme after three years due to ill health, the role was handed over to character actor Patrick Troughton. , official television productions have depicted thirteen distinct incarnations of the Doctor. The longest-lasting on-screen incarnation is the Fourth Doctor, played by Tom Baker for seven years. Within the narrative, these changes were explained as regeneration, a biological process which heals a Time Lord when their incarnation is about to die. Consequently, the Time Lord is given a wholly new body. In "The Deadly Assassin", the concept of a regeneration limit is introduced, giving