Donald Draper wrote:
I find that fascinating but weird too. With that much change what is the common elements that is constant thats makes him feel like the same character?
An interesting question that's been debated in fandom and in various reference books (Doctor Who and Philosophy
for example) for years. Essentially, there are certain core character traits - his wit, intelligence, compassion, eccentricity, morality, anti-authoritarian stance and fondness for Earth and its people - that remain consistent, but each actor puts his own stamp on the part while paying homage to his predecessors (so you can recognise bits of Tom Baker's Doctor in David Tennant's characterisation, and elements of Patrick Troughton's Doctor in Matt Smith's and so forth). It's a bit like James Bond, but with an in-universe explanation. Within the fiction, the process of regeneration
rearranges the Doctor's brain cells and, each time, his memories are jumbled up, resulting in different elements of his personality being brought to the fore.
Each time this happens (1. Hartnell-Troughton 2. Troughton-Pertwee (not actually seen) 3. Pertwee-T. Baker 4. T. Baker-Davison 5. Davison-C. Baker 6. C. Baker-McCoy 7. McCoy-McGann 8.
Unseen 9. Eccleston-Tennant 10. Tennant Smith
), the Doctor goes through a period of (often painful) adjustment, usually involving a period of amnesia or erratic behaviour before he "beds in" to his new persona. It's part of the tradition of the series to follow him getting to grips with his new appearance and personality
, getting to know himself all over again, seeing his new reflection for the first time, choosing his new outfit, etc.
There have been multi-Doctor stories, usually for a milestone anniversary, with various incarnations meeting up through the means of time travel; The Three Doctors
(1972 - the first three Doctors), The Five Doctors
(1983 - the first five Doctors, with Richard Hurndall filling in for William Hartnell, who had passed away by then), The Two Doctors
(1985 - the second and sixth Doctors) and Time Crash
(2007 - the fifth and tenth), with another on the way (at least the tenth and eleventh Doctors) in November for the 50th. These usually serve to highlight the differences between the Doctor's incarnations rather than the similarities, and the interactions between the Doctors are often fractious and played for laughs, despite them being different aspects of the same person; it's like you or me meeting ourselves from 20 years ago and being embarrassed and unable to relate to the people we once were.
The conceptual nature of the Doctor's "change of appearance" was kept vague the first couple of times it happened, until Buddhist Producer Barry Letts coined the term "regeneration" in Jon Pertwee's final story, Planet of the Spiders
, and introduced to the idea an element similar to the Buddhist concept of rebirth
, which has endured.