I find many things endearing about Doctor Who, both on screen and behind the scenes. Being on the show is apparently quite the experience, no less today than fifty years ago; along with the time crunch of working on weekly TV, there's also the budget crunch of working on an episodic show that needs new sets or location filming every week or two, and the technical challenges of working on effects-heavy sci-fi. Days are long, and shooting some of the scripts without any of the SFX creatures to act against can get bizarre. The show has run for so long and become such a cultural institution that the production crew has almost developed its own little society, complete with mores and customs all its own.

One that is seldom if ever spoken of has to do with casting the Doctor. When selecting a new Time Lord, the production team does not generally look for an actor who has a proven track record of playing the kind of Doctor they want -- they look for an actor who in many ways is the kind of Doctor they want, and has a proven track record of playing things larger than life without making the audience hurl tomatoes at the TV. How this particular custom evolved is rather a story on its own.

Here's how it came about:

It's not unusual for a long-running series to deliberately write in character details that take advantage of the actor's own talents. This is how House ended up so musical; the list of instruments Hugh Laurie plays can basically be condensed down to "yes", and he's been known for it at least since he was in the Footlights. Neil Patrick Harris gets to do sleight-of-hand from time to time, because he can and it looks nifty, and also because flash paper is fun to play with. The show gets a gimmick, the actor gets to show off, and the casting director doesn't have to cast a hand/stunt double. Sometimes shows are also written around things the actor has the opposite of talent in, but they're usually not that nice -- Robert Vaughn is distinctly Not Cool with bodies of water much bigger than a Jacuzzi, but that didn't stop Napoleon Solo from getting ignominiously dunked about every other week.

The actor who played the original Doctor, William Hartnell, was fairly old when they started, and inconveniently continued getting older as taping went on. Hartnell was also not a particularly well man; he had a number of health problems that saw him steadily decline over the course of the show, some of which were particularly hard on his short-term memory. After a couple of serials, it got to the point where the main talent he was bringing to the set was the ability to fluff lines he had been prompted on only seconds ago. Television was recorded mostly "as live" in those days, with retakes for anything other than catastrophic technical problems a forbidden luxury, and whiffed lines stayed whiffed on tape all the way out to transmission.

Hartnell was cantankerous, forgetful, and particularly cantankerous about being forgetful, so rather than turn the matter into a power struggle (that the people in favor of Bill Hartnell delivering his lines correctly on the first try would almost certainly have lost), the writing crew simply decided to run with it. It was much easier on both their nerves and their schedule to just decide that the Doctor wanted everyone to think he was a daffy old man, and hope Hartnell didn't lose too many of the lines that hinted he was secretly clever and badass. That worked out reasonably nicely, so they decided that the Doctor was allowed to be ornery as well, because that would also head off any fights over whether Hartnell really needed to look as if he weren't frustrated when on camera.

The flip side of this was that Hartnell could now pretty much expected to be cantankerous all the time, taping or not. This didn't sit very well with the production crew, especially when the Corporation ordered a changing of the guard, and brought in an entirely new group of people for Hartnell to frustrate. When it was finally generally agreed that Hartnell was not well enough to keep working on a demanding show like Doctor Who, the crew had a dilemma on their hands: The character had been tailored to the actor, and no matter how long they searched for a look- and sound-alike, anyone they got was bound to be a bit 'off model' from what Hartnell had been doing.

They solved it, of course, by coming up with the idea of the Doctor regenerating. They also took the opportunity to hire someone considerably less irascible for the role. Patrick Troughton was known professionally for doing a lot of sci-fi and horror -- he had the kind of face that looked particularly serious and spooky when lit from beneath with a small spot -- but as a human being, he had a reputation for being a cheerful practical joker. Particularly infamous is the time he opted to replace his pocket handkerchief with an especially lacy pair of ladies' knickers, and casually tugged them free while on the set; I don't know exactly what the lead in to that was, but it ended with young Deborah Watling blushing furiously and protesting, "But they're not mine!" Troughton was also the first Doctor who had any idea what he was getting into when he signed the contract, and thankfully not the last to enjoy it immensely.

The tradition of picking Doctors according to personality rather than reputation has led to a number of them being cast quite against type. Jon Pertwee was known as a comedian before he took the role, mostly from A Funny Thing Happened On The Way To The Forum and a variety of Carry On films. (He was, however, a former Navy man, and the Third Doctor inherited his love of spy gadgets and things that go vroom directly from the actor.) Colin Baker hadn't much of a reputation for anything before the Doctor; he is nowhere near as pompous as the Sixth Doctor in person, but he certainly is that much of an encyclopedia, and it's not an accident that he's been elected president of the official fan club.

It's fascinating for me to watch all this, as it results in the unusual situation that all of the Doctors are borrowing, quite heavily, from themselves to play the part. It's more apparent for some than for others -- Tom Baker is Tom Baker, obviously and always, and they hired him on exactly that basis. But it can be surprisingly difficult for me to spot the moment when Peter Davison and David Tennant officially break character in the blooper reels; a lot of their body language is the same both as the Doctor and as themselves. The main clue is swearing over biffed lines.