The Doctor is a fictional male Timelord in the Doctor Who series. The character was portrayed on screen by William Hartnell, Patrick Troughton, Jon Pertwee, (Peter Cushing), Tom Baker, Peter Davison, Colin B. The Doctor is a Timelord from the planet called Gallifrey who is able to travel back and forth in time and to other worlds in the universe. The Doctor travels in a spaceship that is said to be infinite in size but on the outside looks like a Police Box. The Tardis looks like a Police Box because it was supposed to be able to blend into the environment but a component broke and chameleon device became locked as a Police Box.
The Doctor nearly always travels with a companion however if it hasn't travelled with one, he'll recruit one when he arrives at his destination. The Doctor companion is always nearly a female. If the companion isn't a female, he'll recruit one to help him wherever he is currently located.
The longest consecutive episodic companion that has been with the Doctor is Jamie. Jamie was first seen in the episode The Highlanders and was last seen in The War Games but he makes a guest appearance in The Two Doctors episode. Since the series came back, Clara Oswald has been the most prolific episode companion so far.
The idea of regeneration came about when the first actor to play The Doctor, William Hartnell announced he wanted to leave so they came up with the idea of regeneration. The Doctor is able to regenerate thirteen times before he dies, however as we near that point, the writers will come up with something to extend his life. We know he does eventually die because in the episode The Name of the Doctor , we visit the Doctor's grave on Trezalore. We won't see his death for years or even decades depending on how successful the series in.
The Doctor never uses a gun to kill his enemies although in an Eleventh Doctor episode, he does use a gun to dislodge something. The Doctor will not go anywhere without his sonic screwdriver, its the Gallifreyan answer to the Swiss Army Knife. Whenever the Doctor needs to take a reading or make something work, the sonic screwdriver will fix it. It did make it a bit too easy for the Doctor that it stopped from appearing for a while.
When the Doctor regenerated, the TARDIS interior and the sonic screwdriver would also change. David Tennant's sonic screwdriver top was blue whereas Matt Smith's screwdriver was green for example. The other doctor's screwdrivers were also different.
In order to save production costs, Third Doctor played by Jon Pertwee stories were confined to Earth. The Storyline had the Timelord enforcing him as punishment. During his time on Earth though, he was able to work with U.N.I.T. to defeat Earth's enemies. It was the first time that The Master, a rival Timelord would make his first appearance in Jon's first storyline, Terror of the Autons.
To get round the planet, he didn't use his trusty TARDIS, instead he used Bessie, a canary yellow roadster. It was specialised make of car, one that was based on the Ford 103E Popular as a base. Ref: Yahoo
Tom Baker is the actor whose held onto the role of the Doctor for the longest. Tom's version of the Doctor is one of the best loved incarnations of the Doctor. Fourth Doctor is famous for his overlong scarf which was made accidentally long by the person who knitted it. Tom Loved the long length of the scarf that he kept it and it became his trademark along with his love of jelly babies which he would offer.
The War Doctor was introduced at the end of The Name of the Doctor as a forgotten Doctor. He appeared for the 50th anniversary episode called Day of the Doctor. The War Doctor happened between the eighth and ninth doctor. The War Doctor was responsible for the disappearance of Gallifrey and the deaths of many which is why the other incarnations of the Doctor forget about him. Since his introduction, all the new doctors have shifted up one.
Matt Smith is the youngest actor to take on the role of the Doctor. He is characterised by his wearing a bow tie which he calls are cool. Such is the influence of the Doctor Who series that when Matt Smith started wearing Bow ties, bow ties sales shot up. In the second series that Matt Smith appeared in, in addition to the bow tie, Matt Smith started wearing a Fez which he also called as cool. The Fez unlike the Bow tie didn't last long as it was shot and destroyed by river Song.