BY RICHARD WHITTAKER

Fact: There are literally dozens of countries that didn't even exist when the first episode of Doctor Who aired in Great Britain. The map of the world has changed since the show started.

The seminal British TV show reaches its 50th anniversary this weekend with the broadcast of a new special, The Day of the Doctor. Finally, after years of teases, fans will find out what the Time War really was. They will see, for the first time since 1985's The Two Doctors, multiple incarnations of the Gallifreyan time-traveler share the screen in continuity. And they will see the continuation of a modern science-fiction mythology, longer lasting than any other of its space-borne siblings.

There is something quintessentially British about the show. It's not just where it's made. It's where it was forged. It's in the story telling, the sense of insularity and exploration, the unabashed intellectualism and the relentless optimism in a dark, unyielding cosmos. Most importantly, it looks on eccentricity as a qualification, not a burden. It's not for no reason that NBC sitcom Community lovingly spoofed it with the whimsical show-within-a-show Inspector Spacetime, and then bemoaned the threat of a tone-deaf U.S. remake.

My personal theory is that the Doctor is, in each incarnation, a different teacher at a mid-century British public school (which really means private school – don't ask). William Hartnell, who originated the character and played the role from 1963 to 1966, was the crusty, fussy, unquestionable school master, a Victorian relic with a sharp tongue and a kind heart. Patrick Troughton (1966–1969) was the deputy head, less practical, more puckish. Jon Pertwee (1970–1974) had the enthusiasm of a biology teacher, always poking at the intriguing and squishy. The Fourth Doctor, Tom Baker (1974–1981) was a classicist and the most literate. Peter Davison (1981–1984) was the cricket-loving geography teacher, fidgety and precise. The underrated Colin Baker (1984–1986) was the permanently enraged maths teacher who had expected to be a university lecturer and now was stuck with teenagers who couldn't do calculus without calculators. Sylvester McCoy (1987–1989) was the political scientist, trying to leaven the darkness with humor, but with flashes of steel underneath.

When the BBC revived the show briefly in in 1996, there was a sea change. Paul McGann's sole performance in a made-for-TV movie recast him as a smouldering, Byronic figure, Gothic and glowering. When the real cash came back for the 2005 revival, Christopher Eccleston followed his lead: His Doctor was a mad scientist, throwing caesium into the cosmic waters, just to see what happened. David Tennant (2005–2010) was a return to the literature department, the bookish, slightly foppish adventurer. And now Matt Smith (2010-2013) is the young drama teacher, trying to convince himself and his friends that bow ties and fezzes are cool.

And that is why you can hear the eye rolling from British people and committed Whovians any time someone refers to the Eccleston run as "season one."

Just as all students have their favorite teacher, everyone has their favorite Doctor. They say it's your first, and I'm just old enough remember Pertwee taking on giant maggots in The Green Death. But for me, it's Tom Baker all the way. The battered hat, the never-ending scarf, the grin that cracked wide as he baffled unstoppable foes with the offer of some Jelly Babies. He was unflappable, as at home facing down killer automata in Victorian London (Talons of Weng Chiang) as space faring lion men (Warrior's Gate). His fellow Time Lords regarded him as a useful menace, the troublemaker they could send to fix their problems. Throughout, he built the mood that, somehow, this would all end up for the best: that we, as a species, would learn something (without the occasional preachiness to which Star Trek was prone).

And soon comes Peter Capaldi, the erudite and aquiline Scot. What, we ask ourselves, will this sinister logician teach us?

The school master metaphor does have its limits. There's a popular misconception that Doctor Who was conceived as an educational show. That, week by week, the mysterious Doctor and his companions would travel to another historic period and try not to change the timeline too much. True, the time-traipsing hero and his ever-revolving coterie of companions visited the Aztecs and the Romans, Cro-Magnon tribes and Victorian tea rooms. But since the second story saw him go toe to axle with his perpetual nemeses, the Daleks, against a post-apocalyptic background, the SF element has always been there.

Not that the show has been a constant. It's actually been killed twice. First, in 1990, when the BBC decided just not to renew for a 27th season. Second, in 1996, when a one-off TV film failed to trigger a true regeneration.

But, like the Doctor himself, it never really died. Even when the BBC pulled the plug, there have been comics, radio dramas, oceans of fan fiction, and disc after disc of original plays on CD fromBig Finish. In part, they were the BBC's own fault. In the early days, copyright and ownership of characters was far more flexible than today's litigious era. Rather frustratingly for Auntie Beeb, they didn't own the rights to the Doctor's great nemesis, the Daleks. Writer Terry Nation did, and he would regularly flaunt that fact at the BBC's expense.

Part of the success and the reason for its diversity is that the time-and-space travelling concept underlying the show meant it could be anything, go anywhere. One week it would be high Gothic. The next, hardcore interstellar sci-fi. Following that would be an adventure with cavemen. It's a part of British lore that the only way to watch the show was hidden behind the sofa, yet many of the actors, like Pertwee and McCoy, came from a comedy background. Each incarnation rewrote the character, but remembered that he was a wanderer: Like the title of the first ever episode, he was "An Unearthly Child," shifting but strangely constant. No other show has ever been granted that flexibility. Even Star Trek, though it would boldly go, would always take the Enterprise with it. Its crew were on a mission of exploration. The Doctor was an explorer. A semantic difference, but vital.

The first show to not simply gloss over its revolving door casting, but to make a story point of it. Throughout it all, the Doctor has always been based around three simple truths. One, he doesn't fight. Two, he doesn't get romantically entangled with his assistants. Three, he's always the smartest being in the room.

Number two has become a little bit tricky in recent years. There was an undoubted hint of a three-way frisson between the Doctor, Captain Jack, and Rose in The Doctor Dances, but that was merely a gateway to the biggest problem with the newest incarnation. Tennant may have been phenomenally popular, and rightly so, but the soap opera elements of his relationship with Rose (Billie Piper) were the biggest misfire. Mercifully, when Smith took the controls of the TARDIS, normality was restored. His Doctor still had an emotional life, but – and here's the really important bit – it didn't involve humans. He still has two great loves – quasi-Time Lord River Song (Alex Kingston) and the TARDIS itself – but (as it was pointed out in earlier incarnations) dating a human would be weird. They are his friends, his companions, or, as one Time Lord glibly put it, his pets.

And this is where that first trait – the non-violence – comes into play. The Doctor is not a pacifist, per se, but a demigod, dabbling and deftly directing the affairs of other species: If monsters, whether human or alien, want to drive themselves to destruction, then he will not stand in their way. But the Doctor never pulls the trigger. Twice he had the chance to end the reign of tyranny and terror of the Daleks. In 1975's Genesis of the Daleks, the fourth Doctor recoils rather than destroy the original breeding chamber: He knows what they can do, but he cannot commit genocide. Then, a decade later, the fifth Doctor held a gun to the head of the creator of the murderous species, Davros, in Resurrection of the Daleks. Yet pulling the trigger is always against his better instincts.

That all changes this weekend. The BBC has explained this new non-Doctor, this warrior, in the brief short prequel Night of the Doctor. As the universe collapses in the Time War, the McGann incarnation realizes that a healer is not needed. he must become the great destroyer, stabilizing what it left of reality. He becomes the War Doctor (John Hurt, glimpsed briefly at the end of last year's Christmas special. And Hell followed with him.

But what the short really revealed is that, across those 50 years, tradition has survived. It's in the hints and references: The women who surround the Doctor are the Sisterhood of Karn, last seen in the seminal and creepy Brain of Morbius. Their voices have been heard in the dramas McGann has done for Big Finish, and in a further nod, the names he lists—Charley, C'rizz, Lucie, Tamsin, and Molly—were his companions on those adventures.

They are, like the Sontarans and sonic screwdrivers, a part of the history of the Doctor. And, after 50 years, the Doctor has to face everything he is not.

This article was originally published in the Austin Chronicle.