Doctor Who
Doctor Who was first shown in 1963, with William Hartnell as the Doctor. When Hartnell left the show in 1966, the writers came up with the idea that the Doctor would regenerate (at the time called renewal) and transform into the Second Doctor, who was played by Patrick Troughton. In 1970, when Jon Pertwee took over as the Third Doctor, the series switched from black-and-white to colour.