Thanks to the new "Doctor Who," there’s still excitement about one of the world’s longest-running science fiction series. In case you’re counting, “Doctor Who” is even older than “Star Trek.”

For those of you not yet in the know, or who only have experience with the current British show, here’s a little primer on the classic series. “Doctor Who” ran continuously on British television airwaves from 1963-1989, logging over 600 episodes. During this time it spawned a theatrical production, an American version, a whole slew of novels that continued after the show was cancelled, a spin-off and later a 1996 Fox/BBC TV movie. “Doctor Who” became such an ingrained part of British culture that Daleks, even before the new series aired, was pretty much a household word.

The outcry that resounded all over the world when “Doctor Who” was cancelled continued until finally, a new series was announced to air in 2005. The excitement surrounding the new series, now featuring Matt Smith and going into its seventh (!!) season, just proves how enduring the Doctor’s appeal has been over the years.

The Story

What’s the secret behind the Doctor’s longevity? Well, he's part of a tradition of British gentleman archetypes (think Sherlock Holmes) - he's good, powerful, eccentric, funny, and super-intelligent, with a touch of loneliness and darkness that clings to him like a shadow. But that doesn't explain it all. Interesting enemies, cute female (and male) companions and science-fiction adventures helped the Doctor become one of the most popular and lasting characters on television.

"Doctor Who" is about a Time Lord, from the planet Gallifrey, who goes around the universe setting things to rights—despite the Time Lords' missive not to interfere with events on other planets. A plot device called “regeneration” allowed continuity; seven actors played the good Doctor during the original series, each of which had eccentric personalities. And each Doctor had scores of mostly younger companions, who followed him on his adventures one or two (or sometimes even three) at a time.

THE DOCTORS

William Hartnell (1963-1966): The first Doctor was doddering, bad-tempered and enigmatic. In the pilot episode, “An Unearthly Child,” he started off the adventures with his granddaughter Susan and two of her teachers, Ian and Barbara, in the Stone Age. He stayed through four seasons. Victoria, Dodo and Jamie were among his other companions.

Patrick Troughton (1966-1969): A much-loved favorite of fans, the second Doctor was a cosmic hobo with baggy trousers, twinkling eyes and a wonderful sense of humor. He brought a softer side to the Doctor’s irascible intelligence. His companions included Zoe, Jamie, Polly and Ben.

Jon Pertwee (1970-1974): Ah, finally most episodes are in color. And the new Doctor—rather a dandy, with his capes and his yellow roadster and a little bit of a lisp—hooks up with UNIT. Supporting characters include General Lethbridge-Stewart and his UNIT co-horts, such as Sergeant Benton. His companions included Jo, Liz Shaw, and the extremely popular Sarah Jane Smith. Actress Elisabeth Sladen, who played Sarah Jane, went on to reprise the role in several episodes, plus the spin-offs "K-9 and Company" and "The Sarah Jane Adventures" from 2007-2011. Sladen died in April, 2011.

Tom Baker (1974-1981): The first doctor discovered by many American audiences through airings of “Doctor Who” on PBS, he was also the most enduring and arguably the most popular of the classic series. Described as all teeth and curls, his trademark was his long, multi-colored scarf and his love for a soft, gummy and fruity English candy called jelly babies. His companions included Leela the savage and Romana the Time Lady. His tenure included the “Key to Time” episodes, a continuing epic of six stories that made up one season.

Peter Davison (1982-1984): One of the editor’s personal favorites. Consider him the pleasant one, the cricketer of the bunch. His trademark was the piece of celery he always wore on his lapel (to notify him of radiation in the atmosphere). His companions included Tegan, Nyssa and the tragically-destined Adric.

Colin Baker (1984-1986): Probably the least popular Doctor, thanks to his brash manner. He always wore a multi-colored coat, and his second year was another season-long story arc called “Trial of a Time Lord.” His companions, too, were more annoying than not: Peri, the breasty screaming "American", and Mel, who was always making the Doctor drink carrot juice.

Sylvester McCoy (1987-1989): Another favorite Doctor for his congeniality and mystery, with a Panama hat, a question-mark umbrella and sweater vest. He was the last Doctor to star in the series when it was cancelled in 1989 (after a long battle with the BBC). His major companion was Ace, who called him “Professor.” She was the baddest of his companions, being a school dropout who knows a lot about bombs.

After the series ended, the Seventh Doctor and his companion Ace were featured in an ongoing series of novels that took a much darker tone. Then, in 1996, the Eighth Doctor appeared in an American TV movie:

Paul McGann (1996): The Doctor crash lands in America; a Dr. Grace Holloway, who is puzzled by his two heartbeats, operates on him and actually kills him, causing him to regenerate into his eighth incarnation. He chases the Master.

Over the years there have been a few other Doctors in movie productions and such; but we won't list them here in the interest of brevity. They're not considered part of the official Doctor Who timeline.

THE ENEMIES

Over 20-odd years, the Doctor has come up against some fascinating enemies. Here’s a short list, although of course it’s impossible to put down here all the delectable baddies he’s triumphed over during the course of several decades:

The Master: Think of him as the anti-Doctor. Like the Doctor, the Master is a renegade Time Lord who interferes in other worlds’ events. However, the Master is evil. And he’s close to the end of his 13-regeneration cycle, which means he has to go to amazing lengths to keep himself alive.

The Daleks: These evil machines house tiny green lumps of flesh. And even though their vocabulary is limited (“I obey” and “Exterminate” seem the extent of it), and even though they didn’t walk up stairs until the mid-‘80s, they and their creator Davros continue to plague Doctor Who for years—and no new series would be complete without them. In the new series, the Daleks have become more menacing and less limited physically, but the original ones will always hold charm for true fans.

The Cybermen: These silver robot guys were just mean. They liked to invade Earth a lot; they’re from its twin planet (an evil planet, of course) Mondas. It turns out that they’re allergic to gold. Naturally, the new series has featured them liberally as well.

The Time Lords: Okay, technically the Time Lords aren’t bad, they’re neutral. But they admittedly find the Doctor’s penchant for interfering to be useful sometimes, and they’re not above using him for their own ends, especially for the good of Gallifrey. By the time the new series has rolled around, the entire civilization has been decimated.

TRIVIA

Other tidbits you might want to know about classic Doctor Who (WARNING: SOME SPOILERS):

1. The special effects were bad even in their own day, thanks to a virtually non-existent budget. Imagine, if you will, creating a green lumpy monster by wrapping someone with green-painted bubble wrap. They did that. Yes, this show was famous for its cheesy effects.

2. The TARDIS, the Doctor’s blue police box spaceship that’s bigger inside than out, stands for Time And Relative Dimensions in Space. It’s supposed to take on the shape of something native to the environment where the ship lands, but that part of the ship doesn’t work anymore. The Doctor stole the TARDIS when he first started traveling—and whether or not he actually understands its workings is anybody’s guess.

3. Although in general the tone of the show was lighthearted, two of the Doctor’s companions died. Katarina, who traveled briefly with the Doctor in 1965, was a maiden from ancient Troy who felt completely bewildered by the TARDIS. After just a couple of episodes, she was taken prisoner by a psychopath, then sacrificed herself so the Doctor could get away from the Daleks. Adric, who traveled with the fifth Doctor, died while trying to stop a spaceship from destroying Earth—and fails. As it turns out, this spaceship is what killed the dinosaurs.

4. Several episodes, “The Five Doctors,” “The Three Doctors” and “The Two Doctors,” put many of the actors together in the same episode. These were special, of course. The best of these is surely “The Five Doctors,” which featured every regeneration through Peter Davison—although William Hartnell was deceased by this time, and replaced by anther actor, and Tom Baker could not return, so was featured in clips of unaired footage. Now that the show is nearing its 50th anniversary, many fans are hoping for a reunion along the same vein, featuring the doctors from the new series.

5. There are lost episodes of early “Doctor Who.” Over 100 from the '60s at last count, thanks to an archive purge by the BBC in the '70s. When you’ve produced a series since 1963, before the advent of VCRs, many of which had multi-part episodes, you’re bound to lose a few, although the loss seems tragic and unfathomable today. We can only hope that some show up someday--there has been a case or two in which a tape was found recently.

6. Currently, many episodes of classic “Doctor Who” are out in DVD, but not in any comprehensive form. In fact, most are just single stories made up of multi-part episodes (maybe five half-hours at the most), and the first and second Doctors are vastly underrepresented. However, they have released some "lost" episodes singly, which we appreciate. But we’re still waiting for the BBC to smarten up and release everything they’ve got by season!

7. Originally, the series aired late afternoon on Saturdays in the U.K. Many families would gather together to watch the half-hour show during their dinner hour. As it was designed to be scary to nine year olds, many children watched "Doctor Who" from behind the couch. Americans mostly discovered the show from airings on PBS in the 1980s, which varied locally.

Editor's Note: This article was first written in 2005, in advance of the debut of the new "Doctor Who," and has been updated.