Today in 1964 The Dalek Invasion of Earth concluded with the episode entitled Flashpoint. This ended with the departure of the Doctor's granddaughter Susan. Carole Ann Ford was the first star of the show to want to leave it, disliking the lack of characterisation for Susan. She had been promised something more akin to an Avengers companion, with special powers. William Hartnell delivered a wonderful farewell speech to her - which was subsequently reused at the beginning of The Five Doctors in 1983, and was both repeated and recreated for An Adventure in Space and Time in 2013.
"One day, I shall come back. Yes, I shall come back. Until then, there must be no regrets, no tears, no anxieties. Just go forward in all your beliefs, and prove to me that I am not mistaken in mine. Goodbye Susan. Goodbye my dear."