This episode, and the next one, The Unknown People: Part II (#1.26), was originally part of theatrical film Superman and the Mole-Men (1951). The producers of the series later edited the film into episodes of the show.
This is the first of only two episodes in the series in which Jack Larson and John Hamilton are not listed on the credits.
This episode is Part I of the only two-part (or multi-part) episode in the entire series.