TV plots changed because of off-screen drama
With the exception of a 16-year gap from 1989 to 2005, Doctor Who has been running since 1963. While most long-running TV shows involve a lot of cast replacements, Doctor Who has kept the same main character at its forefront for more than 50 years. How?
Well, “The Doctor” is a 900-year-old alien “Time Lord” who uses a time-traveling police box called the TARDIS to traverse space and time with relative ease. Once in a while, all that travel catches up with the doctor, and he must shed his human form and take on a new one. In the world of the show, that’s called “regeneration,” and it’s always an emotional moment when the doctor changes, say, from David Tennant into Matt Smith or from Peter Capaldi into Jodie Whittaker. Regeneration is a major part of the elaborate Who mythos, but it came about as a clever solution to a big problem.
In 1966, the first doctor, 58-year-old William Hartnell, had to leave the show because of health problems. Producers didn’t want to end the series, but they didn’t know how to replace the star. Then they realized that the main character was an alien, so anything was possible. Result: Hartnell’s doctor regenerated into actor Patrick Troughton’s doctor.