Edward Burnham portrays Professor Kettlewell, the wild-haired, bespectacled boffin who creates the titular K1 robot. Along with Courtney and Levene, Burnham had also appeared in "The Invasion", where he played another scientist, Professor Watkins. The part of the K1 robot is played by Michael Kilgarriff who had played another robotic part in "The Tomb of the Cybermen" (1967), the Cyberman Controller. Patricia Maynard is cast in the part of Miss Hilda Winters, the director of the National Institute for Advanced Scientific Research. Miss Winters' assistant, Arnold Jellicoe, is played by Alec Linstead. Linstead had played the part of Sergeant Osgood—a member of the technical staff at UNIT—in "The Dæmons" (1971).