Doctor Who, BBC One (UK)
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Incredibly long-running, classic sci-fi television series from Britain, one of the greatest TV series of all times. There were seven different Doctors in the course of the (original) series, which ran for 26 seasons (or series, as of course they say in the UK), from 1963-1989. Well... I suppose first I should say that we don't know the Doctor's name, he's just called the Doctor, although an old friend of his once called him Theta Sigma. Not that that means it was his name, or anything. I'd rather not know his real name, anyway. Um, the Doctor is a Time Lord, from planet Gallifrey. His race developed time travel long ago. They regenerate, too. They'll live a full life, then regenerate. They're only supposed to be able to do this like 12 times or something. But they can live hundreds and hundreds of years because of this (though actually I think they can live hundreds of years within a single generation). Anyway, this gives different actors a chance to play essentially the same role. Except that it's not just appearance that changes when Time Lords regenerate, their whole personalities can change, everything from sense of humor to fashion sense, and so on.... But one thing that will never truly change about the Doctor is his sense of adventure, his generally maverick nature which sets him apart from the other Time Lords, and keeps him away from his homeworld the vast majority of the time. Though I suspect one day he might come to wish he'd spent a bit more time there.... But that's getting a few decades ahead of myself!
Anyway, the Doctor has a tardis, which stands for "time and relative dimensions in space." On the outside it looks like a British police box (similar to a phone booth). The Doctor's tardis's chameleon circuit is busted, which is why it can't change appearance as most tardises can. Anyway, inside it's really huge, because of a dimensional stablilizer that lets the inside be bigger than the outside. Usually we just see the control room, which is right inside the door. But there are lots of other rooms, many of which are very large. You could get quite lost in there. Anyway, a tardis is a vehicle which lets one travel through time and space, but not really like a ship, exactly. The Doctor goes to lots of different times and places both on Earth and throughout the universe. He gets involved in all sorts of trouble and manages to save the day, whatever's going on. There are lots of recurring enemies such as the Master, who is an evil renegade Time Lord; a robotic race called Cybermen, a robotic race called Daleks, and um... plenty of others.
The Doctor almost always has companions with him. He's had lots of companions over the years, way too many to mention here, but some of my favorites included Ace, Leela, K-9, and Adric. I should say we quite liked many, if not most or all of his female companions. Quite. Quite. Anyway... the fourth Doctor, played by Tom Baker, is generally considered the best. That's because he was. Oh, Connery doesn't have to be your favorite Bond, but Tom does have to be your favorite Doctor, or else you're just plain wrong. I'll leave second favorite up to you; mine's the seventh, played by Sylvester McCoy. But really, I think they're all fairly okay. Though I'm not greatly familiar with the first or especially the second.
Actually, there's also an eighth Doctor, but he was just in a TV movie (BBC; IMDb; Wikipedia) in 1996, which could have spawned a new series, but didn't. One day I'll have to try to watch it again and write up a review, I guess. Meanwhile, I fear I haven't been saying enough about the classic series. I just don't really know how to do it justice, and I certainly can't, in the space I'm willing to give to this entry at present. Of course I haven't seen nearly all of the series, and I don't remember what I have seen quite as well as I'd like. And anyway, the props and special effects and things could be rather cheesy. But still, I love the show, and it deserves a better description than I can give. So I guess it's a good thing I've provided plenty of links to other sites, which do a far better job than I ever could (particularly some of the ones on my "Doctor Who links" page)....
Of course, there have been plenty of specials and things over the years (some probably canonical and some surely not). And I certainly haven't seen nearly all of them. There was a special between seasons 20 and 21, called The Five Doctors. And there was a spin-off series, K-9 and Company, which only had one episode produced. And there was a spoof called The Curse of the Fatal Death. And in 2013, there was a TV movie called An Adventure in Space and Time, a docudrama about William Hartnell's time as the first Doctor.
Doctor Who was once again revived in 2005, with the ninth Doctor. Some folks reckon it as the same series, even after a 16-year "hiatus" (discounting the TV movie), starting with series/season 27 onward; while others consider it a new series altogether, though everyone considers it the same continuity. I essentially consider it the same series, but in other ways it's more convenient to think of it as a new series, so I've got a separate page for it (later divided into several pages). There's also a show spun off of that, called Torchwood.