Let’s be honest. If you’re a fan of the show today, you’re used to the fireworks. You expect the golden energy, the exploding TARDIS, and the tearful "I don't want to go" speeches. But back in 1966? Nobody had a clue. When William Hartnell collapsed on the floor of the TARDIS at the end of The Tenth Planet, the audience didn't think they were witnessing a clever sci-fi trope. They thought the show was dying.
The Doctor Who first regeneration wasn't some grand, planned-out piece of lore. It was a desperate, last-minute gamble to save a hit show from a medical crisis.
The Messy Reality Behind the Scenes
William Hartnell was the Doctor. Period. To the kids watching in the sixties, he wasn't "The First Doctor"—he was just The Doctor. But behind the curtain, things were falling apart. Hartnell was suffering from arteriosclerosis. It’s a nasty condition that, for him, meant he was struggling to remember his lines. He was getting "doddery," as some of the crew put it. He was also, by many accounts, becoming increasingly difficult to work with as his health declined and the original production team he loved began to move on.
The BBC had a massive problem. The show was a juggernaut, but its lead actor couldn't keep up with the grueling 40-plus episodes a year schedule.
They actually tried to replace him earlier. Producer John Wiles wanted to swap Hartnell out during The Celestial Toymaker by having the villain make the Doctor invisible and then "reappear" with a different face. The BBC bosses vetoed it. They thought it was too weird.
But by the time Season 4 rolled around, there was no choice. Hartnell and the new producer, Innes Lloyd, reached an agreement: he had to go.
It Wasn't Even Called "Regeneration"
If you went back to 1986 (the year The Tenth Planet is actually set in) and told a fan about "regeneration," they’d look at you like you were speaking Gallyfregian. The term didn't exist yet.
In the original script, they called it "renewal."
The idea, spearheaded by script editor Gerry Davis and Innes Lloyd, was that the Doctor was an alien whose body could basically refresh itself. It was meant to be a "biological rejuvenation." The theory was that as he got old, he could just... shed the old skin. Like a snake. Sorta.
Actually, the early concept was even weirder than what we have now. They described it more like a "bad trip" or a psychological breakdown. The Doctor would be confused, his personality would flip, and he’d physically become younger. It was a way to keep the show going forever without ever having to explain why the lead actor was suddenly 30 years younger with a bowl cut.
What Actually Happened in The Tenth Planet?
The story itself is famous for introducing the Cybermen, but most people forget the actual plot because they're just waiting for the end. The TARDIS lands at the South Pole. There’s a "twin" planet of Earth called Mondas. The Cybermen are trying to drain Earth's energy.
Throughout the four episodes, the Doctor is clearly fading. In fact, Hartnell was so ill during filming that he barely appears in Episode 3. They had to rewrite the script on the fly, having the Doctor collapse early so the other characters could carry the weight.
Then came the moment.
October 29, 1966. Episode 4. The Doctor defeats the Cybermen (barely) and stumbles back to the TARDIS. He looks terrible. He's pale. He's weak. He falls to the floor. Ben and Polly, his companions, watch in horror as his face begins to glow with a strange, flickering light.
And then? He’s Patrick Troughton.
It lasted about ten seconds. No dialogue. No "moment has been prepared for." Just a quick cross-fade and a very confused audience.
The "Lost" History
Here is the kicker: that historic moment? It’s technically lost.
The BBC, in their infinite wisdom back then, wiped the master tapes for The Tenth Planet Episode 4. We don't have the original broadcast version of the full episode. We only have the regeneration scene because a fan recorded it on a 16mm camera or it was used in an episode of Blue Peter.
Think about that. One of the most important moments in television history survived because of a kids' show clip and some luck.
Misconceptions You Probably Believe
We’ve had sixty years to over-analyze this, and in doing so, we’ve projected a lot of modern "rules" back onto the 1966 version that just weren't there.
- The Time Lord Rule: At this point, the Doctor wasn't even a "Time Lord." We didn't learn that until The War Games in 1969. In 1966, he was just a mysterious space traveler.
- The 12-Regeneration Limit: This wasn't a thing until 1976 (The Deadly Assassin). When Hartnell changed, the producers thought he could probably do this forever.
- The "Death" of the Doctor: Nowadays, we treat regeneration like a death. Back then, it was treated as a literal medical recovery. He was just "getting better."
Why It Still Matters
The reason Doctor Who is still on your TV in 2026 is because this specific gamble worked. If the audience had rejected Patrick Troughton, the show would have been cancelled by Christmas 1966.
But Troughton was brilliant. He didn't try to imitate Hartnell. He went the "Cosmic Hobo" route—baggy pants, recorder, playing the fool while being the smartest guy in the room. By changing the personality so drastically, the show proved that "The Doctor" was an idea, not just a person.
✨ Don't miss: Big Spring TX Theater: Why Locals Still Love the Cinemark 4
The first regeneration wasn't a masterstroke of storytelling. It was a "fix-it" for a sick actor. But it accidentally gave the show the secret to immortality.
What you should do next
If you want to actually see this piece of history, you don't have to hunt down grainy bootlegs. The BBC released an official animation of The Tenth Planet Episode 4 to fill in the gaps of the missing footage. It uses the original audio (which survived) and pairs it with modern animation. It’s the closest you’ll get to experiencing the shock of 1966 without a time machine.
Go watch the 2013 drama An Adventure in Space and Time as well. David Bradley plays Hartnell, and it captures the heartbreaking reality of why he had to leave the role he loved. It puts the "sci-fi" transition into a very human perspective.