"The entire point of 'Doctor Who,'" as the series' current showrunner Steven Moffat once told me, "is to frighten children." 50 years ago this weekend (a very special episode debuts Saturday at 2:50 p.m. on BBC America, at the same time it's airing around the world), the series debuted on the BBC in the hopes that a mysterious time traveler called the Doctor — and, later, pepper pot-shaped aliens called the Daleks, unstoppable steel Cybermen, lizard people and more — would excite the youth of the UK.

That the series has endured this long — give or take a 16-year hiatus in the '90s and early '00s — speaks to the elegant genius of the idea, to the talents of the men and women who have been responsible for telling the Doctor's stories over the years, and for the power of childhood imagination. Over the years, I've met many, many "Who" fans who can describe in elaborate detail the first episode they saw as a kid, how old they were and what kind of pajamas they were wearing as they huddled close to their mom and dad while the Daleks shrieked "EXTERMINATE! EXTERMINATE!" They stuck with the series into adulthood, and/or came back to it when producer Russell T. Davies revived it eight years ago, and love it as dearly for how it reminds them of those childhood thrills as for what it has to offer them as grownups.

That was not my experience. When I was of the perfect "Who"-acquiring age, my local PBS station was showing the Tom Baker seasons (I didn't catch his name back then, but the hair and enormous scarf were impossible to miss), and I would occasionally stumble across one during afternoon channel-surfing. At the time, I found the Daleks weird and off-putting, and the show's unrelenting cheapness — not just the cramped and primitive sets, but the harsh-looking videotape on which the old episodes were shot — even moreso. Though I was a massive nerd of many flavors, this was one I simply didn't acquire the taste for.
 
Then came the Davies revival, which I sampled mainly out of professional curiosity. In part by moving the production to Wales, Davies was able to wrangle a respectable production budget; the new version will never be mistaken with "Game of Thrones" or "Boardwalk Empire," but no longer does it look like a home movie filmed in your uncle's walk-in closet.(*) Christopher Eccleston was the latest Doctor, a brooding sort consumed with guilt and grief over killing his entire race in order to end a war in time that would have otherwise destroyed all of reality. With this move, Davies gave new pathos to his new Doctor, and also streamlined (for a while, anyway) the entire series: one man, one TARDIS (the police call box-shaped machine that allows the Doctor and his companions to travel through time and space), and limitless possibilities for where and when stories could go.

(*) After falling for the Davies version of the show, I decided to give the vintage episodes another try. I watched the Tom Baker-era "City of Death" — held up by many fans as the best classic "Who" story arc (or, at least, the best arc that doesn't require years and years of backstory)
ever, and it felt like a chore to get through to the end, especially after I had experienced a version of "Doctor Who" that moved so briskly and looked at least competent. 

It was a perfect jumping-on point, a perfect way for fully-grown fans of the series to introduce it to their own children, and a deft blend of old and new. The sharper look and faster pace mixed in with the fantastic ideas and unapologetic melodrama to create a treat for any age, and the modern "Who" has unsurprisingly become an enormous crossover hit in the UK, even as it largely remains a cult curiosity here.

Eccleston only stayed for one year, replaced by the man many fans new and old consider the best Doctor of them all: David Tennant, gangly and yet dashing, quirky and yet terrifying when he wanted to be, expertly playing to the kids in the audience, but also to their parents and grandparents.

Over the course of the Davies years, the Doctor would take us to the literal end of the Earth, to London during the Blitz, to the court of Versailles, to the city of Pompeii on the day Mt. Vesuvius erupts, and to alien worlds with all manner of odd (or Ood) creatures to bedevil the Doctor and his friends. Moffat, the series' current caretaker after writing several episodes during the Davies era, demonstrated a particularly creepy aptitude for inventing monsters that would terrify viewers of any age, most famously the Weeping Angels, a collection of stone gargoyles that operate on a fiendishly simple set of rules: they can only move (and hurt you) when you aren't looking at them.(**)

(**) For more on the Weeping Angels and other modern "Who" highlights, check out our list below of some of the best contemporary episodes.

Both Davies and Moffat made the human companions — including Billie Piper as bored shopgirl Rose, Freema Agyeman as lovestruck Dr. Martha Jones, Catherine Tate as hilariously blunt Donna Noble and Karen Gillan as fearless Amy Pond — into characters so rich that they were often just as big a draw as the Doctor himself. Each season is structured as a puzzle, with standalone adventures that all eventually tie into some larger threat that threatens the whole of existence and/or the immortal Doctor (currently played by wiry young Matt Smith, who is soon to be replaced by acidic Scottish actor Peter Capaldi) himself.

Whether run by Davies or Moffat, the revived "Doctor Who" is a wonderful blend of genres and styles. The TARDIS can take the Doctor anywhere, or when, and the show can become anything it likes, to suit the strengths of its actors and its creative team. (The one season Tennant and Tate worked together, for instance, featured a lot more overt comedy.) Both Davies and Moffat have certain writerly tropes that they each would repeat over and over until they lost their effectiveness (hopefully, Capaldi's arrival will reinvigorate Moffat), but like the Doctor himself, the men and women in charge of writing the show can always be replaced by someone else.

It's a series of limitless possibilities, and though I didn't come to love it until adulthood, I often feel like a kid as I watch it, during both the scary and the thrilling parts.

Alan Sepinwall may be reached at sepinwall@hitfix.com