10 TV Episodes That Broke All The Rules

10. The Tenth Planet: Episode 4 - Doctor Who

Regeneration is one of the defining traits of British sci-fi classic Doctor Who..

The ingenious idea to give Time Lords the ability to change their faces and bodies when they are sick or wounded was first invented to get around the failing health of William Hartnell, the first actor to play the Doctor.

Hartnell's final bow came in the finale of the four-part serial, The Tenth Planet, in 1966. Throughout his battles with the Cybermen, the Doctor grows weaker and weaker, eventually succumbing to old age at the end of the episode. His first body dies and he is reborn with a new face and a new actor, Patrick Troughton.

This episode completely changed the game when it came to the format of Doctor Who. The show had given itself the ultimate get out of jail free card - if an actor playing the Doctor gets sick or wants to quit, then the showrunners can just hire a new one without disrupting the continuity of the show.

It's a brilliant idea that has kept Doctor Who on TV for decades and will keep it going for decades more to come.