The Day the Earth Stood Still was a science fiction film released during the mid-20th century. The plot centers on a fictional postulation of what Humanity's first contact with an alien race would be like. Although the alien that arrives on Earth is a benevolent ambassador with essentially peaceful intentions, the mass public reacts with hysteria and paranoia at his arrival.
In Captains' Logs: The Unauthorized Complete Trek Voyages, Michael Piller calls the basic plot of TNG: "First Contact" an homage to this film, only "we're the aliens".
It is interesting to note that although Klaatu's mission (the main character in the film) is to deliver to Earth a forceful warning against "extending your aggression beyond your planet," he asserts that those he represents have no interest in how Humans manage their own affairs. This assertion is an early progenitor of Starfleet's eventual General Order 1.
The Spanish title for the movie is Ultimátum a la Tierra (Literally "Ultimatum to Earth"), not being known for its original title. However, in the dubbed version of episode "Cogenitor", Tucker translates the original, literal title ("La Tierra Se Detuvo", literally "The Earth Stood Still").
Later, Tucker explains it is a fiction ("In fact, the Earth did not stand still"), keeping the literal translation, but adding confusion to a Spanish-speaking audience that might not be familiar with the original title.