Premise: "Klaatu barada nikto" is a phrase that originated in the 1951 science fiction film "The Day the Earth Stood Still". The humanoid alien protagonist of the film, Klaatu (Michael Rennie), instructs Helen Benson (Patricia Neal) that if any harm befalls him, she must say the phrase to the robot Gort (Lockard Martin). In response Gort relents from destroying the Earth and resurrects Klaatu from death.
Hypothesis: "Klaatu barada nikto" is a phrase that didn't exist before 1951.