"The Krotons" was the first contribution by Robert Holmes to Doctor Who (1963). He would later be regarded by fans, critics and peers to be the show's best writer and script editor.
Robert Holmes had originally submitted this story to the BBC as a stand-alone science-fiction serial in 1965. Head of Serials Shaun Sutton rejected the serial as being not the kind of thing the BBC was interested in making at the time, but suggested the writer pitch it to the Doctor Who (1963) production office as an idea for that series. Holmes did so, and although story editor Donald Tosh was interested, the scripts went no further at the time. Some years later, assistant script editor Terrance Dicks found the story in the production office files when clearing a backlog, and decided to develop it with Holmes as a personal project, in case other scripts fell through.
This episode was watched by 9 million viewers on its original transmission, making it the highest rated episode from the Patrick Troughton era.
Working titles for this story included "The Trap" and "The Space Trap" .