Fifty years ago today — one day after John F. Kennedy was assassinated — a science fiction show about an alien doctor who travels through space and time premiered on the BBC.

At the time, those behind Doctor Who expected dismal ratings because they didn’t think audiences would tune in following the news of JFK’s death.

But the show’s premiere on Nov. 23, 1963 garnered 10 million viewers in Britain. Today the show’s viewership sits at 77 million people worldwide.

“It was just exciting,” Peter Davison, who played the fifth incarnation of The Doctor from 1981 to 1984, told Day 6 host Brent Bambury.

“I mean, there had never been anything like it that I can remember … It was such a simple idea and just so wonderfully attractive to young boys and girls.”

Doctor Who follows a time-travelling humanoid alien known as The Doctor who voyages through the universe on a ship called TARDIS. When he sustains a fatal injury, he doesn’t die — he regenerates, and a new actor steps into the role.

“The idea that you’re given Doctor Who really is that you’re cast to be different from your predecessor,” Davison said.

Dalek Doctor Who

Sophie Sheaf , 12, looks at a Dalek, a character from the popular British BBC science fiction TV series Doctor Who. The Daleks are returning in Saturday's special 50th anniversary episode. (Max Nash/Associated Press)

Fans of the show will be in for a treat when the special 50th anniversary episode airs on Saturday — the return of the Daleks, a race of evil cyborgs.

Davison says acting alongside the Daleks was “much scarier” than he’d anticipated.

“I always imagined they’d be fairly ineffective,” he said.

“In fact, they move just about the quickest of any Doctor Who enemy. They really do race down those corridors and they’re much bigger than you imagine, as well.”

Davison’s final episode, The Caves of Androzani, was voted best episode in a poll by the official Doctor Who magazine in 2009.

The 50th anniversary episode’s global simulcast airs in Canada on the SPACE channel at 2:50 p.m. ET on Saturday.