This story was largely inspired by King Kong (1933) in its portrayal of sympathetic monster. Isaac Asimov's "I, Robot" also served as an inspiration.
Nicholas Courtney later regretted the length of his hair in this story. His hair was cut for his next appearance in Terror of the Zygons: Part One (1975).
This was the first serial in which location scenes were shot using Outside Broadcast videotape instead of film. This was made possible by the introduction of lightweight video cameras. This also made it possible for the robot to grow in size later in the story more successfully. Producer Barry Letts had also been very dissatisfied with the dinosaurs in the previous season's Invasion of the Dinosaurs: Part Two (1974), when there had been a very obvious clash between filmed backdrops and model dinosaurs shot on video.
Tom Baker was recommended for the role of the Fourth Doctor by William Slater. Producer Barry Letts and script editor Terrance Dicks then went to see him in The Golden Voyage of Sinbad (1973), which convinced Letts he was right for it.
Parts of this story were recorded at the same time as parts of "Planet of the Spiders". This not only meant that Jon Pertwee and Tom Baker were literally playing the Doctor at the same time, but also that Elisabeth Sladen and, to a lesser extent, Nicholas Courtney and John Levene were rushing back and forth between the two productions.