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###Input: Twelve actors have headlined the series as the Doctor. The transition from one actor to another is written into the plot of the show, as well as the differing approach to the role that each brings, under the concept of regeneration into a new incarnation. The show's premise is that this is a life process of Time Lords through which the character of the Doctor takes on a new body and, to some extent, new personality, which occurs after sustaining an injury which would be fatal to most other species. Each actor's portrayal differs, but they are all intended to be aspects of the same character and form part of the same storyline. The time-travelling nature of the plot means that, on occasion, different Doctors have met each other. Peter Capaldi took on the role after Matt Smith's exit in the 2013 Christmas special "The Time of the Doctor".

Doctor Who follows the adventures of the primary character, a rogue Time Lord from the planet Gallifrey, who simply goes by the name "The Doctor". He fled from Gallifrey in a stolen Mark I Type 40 TARDIS – "Time and Relative Dimension in Space" – time machine which allows him to travel across time and space. The TARDIS has a "chameleon circuit" which normally allows the machine to take on the appearance of local objects as a disguise. However, the Doctor's TARDIS remains fixed as a blue British Police box due to a malfunction in the chameleon circuit.

The Doctor rarely travels alone and often brings one or more companions to share these adventures. His companions are usually humans, as he has found a fascination with planet Earth. He often finds events that pique his curiosity as he tries to prevent evil forces from harming innocent people or changing history, using only his ingenuity and minimal resources, such as his versatile sonic screwdriver. As a Time Lord, the Doctor has the ability to regenerate when his body is mortally damaged, taking on a new appearance and personality. The Doctor has gained numerous reoccurring enemies during his travels, including the Daleks, the Cybermen, and the Master, another renegade Time Lord.

Doctor Who first appeared on BBC TV at 17:16:20 GMT, eighty seconds after the scheduled programme time, 5:15 pm, on Saturday, 23 November 1963. It was to be a regular weekly programme, each episode 25 minutes of transmission length. Discussions and plans for the programme had been in progress for a year. The head of drama, Canadian Sydney Newman, was mainly responsible for developing the programme, with the first format document for the series being written by Newman along with the head of the script department (later head of serials) Donald Wilson and staff writer C. E. Webber. Writer Anthony Coburn, story editor David Whitaker and initial producer Verity Lambert also heavily contributed to the development of the series.[note 1] The programme was originally intended to appeal to a family audience, as an educational programme using time travel as a means to explore scientific ideas and famous moments in history. On 31 July 1963 Whitaker commissioned Terry Nation to write a story under the title The Mutants. As originally written, the Daleks and Thals were the victims of an alien neutron bomb attack but Nation later dropped the aliens and made the Daleks the aggressors. When the script was presented to Newman and Wilson it was immediately rejected as the programme was not permitted to contain any "bug-eyed monsters". The first serial had been completed and the BBC believed it was crucial that the next one be a success, but The Mutants was the only script ready to go, so the show had little choice but to use it. According to producer Verity Lambert; "We didn't have a lot of choice — we only had the Dalek serial to go ... We had a bit of a crisis of confidence because Donald [Wilson] was so adamant that we shouldn't make it. Had we had anything else ready we would have made that." Nation's script became the second Doctor Who serial – The Daleks (a.k.a. The Mutants). The serial introduced the eponymous aliens that would become the series' most popular monsters, and was responsible for the BBC's first merchandising boom.

The BBC drama department's serials division produced the programme for 26 seasons, broadcast on BBC 1. Falling viewing numbers, a decline in the public perception of the show and a less-prominent transmission slot saw production suspended in 1989 by Jonathan Powell, controller of BBC 1. Although (as series co-star Sophie Aldred reported in the documentary Doctor Who: More Than 30 Years in the TARDIS) it was effectively, if not formally, cancelled with the decision not to commission a planned 27th series of the show for transmission in 1990, the BBC repeatedly affirmed that the series would return.



###Question: How many actors have played Doctor Who?

###Answer: {'answer':'Twelve'}