->''[[MemeticMutation Klaatu...]] [[KlaatuBaradaNikto barada... nikto.]]''

'''''The Day The Earth Stood Still''''' is a 1951 black-and-white science fiction movie based on the short story ''Farewell to the Master''. The HumanAlien Klaatu lands in Washington DC (in a classic [[FlyingSaucer flying saucer]]) during the ColdWar era. The paranoid military shoots him, prompting his [[KillerRobot robot]] Gort to go on a rampage. Klaatu stops Gort, then tells the President of a message for all the world's leaders (who can't agree on a meeting place). Klaatu later escapes to live among the people of Earth and learns of their penchant for war -- but also of their message of peace and understanding.

As a demonstration of power, Klaatu freezes everything mechanical in the entire world (except for airplanes in flight and hospital electronics) for exactly half an hour. (This is the event referred to in the title, though nobody calls it such within the story.) The military takes this as a sign of hostile intent and responds by hunting Klaatu down and killing him. Shortly before they catch up with him, Klaatu gives one of his newfound human friends, Helen, a message to deliver to Gort in his own language: "[[KlaatuBaradaNikto Klaatu barada nikto]]." Gort re-activates upon Klaatu's death and begins destroying the city, but Helen's message diverts Gort into retrieving Klaatu's body. The robot temporarily revives Klaatu, who tells the people of Earth of Gort's true purpose: he, and other robots like him, were built to enforce peace in the galaxy -- and if humans bring their warlike ways into space, they will be destroyed. Klaatu leaves Earth with a simple phrase to mull over: "The choice is yours."

This film's plot was copied in the extremely similar (yet [[NarmCharm hilarious]]) ''Film/Plan9FromOuterSpace''.

There was a [[Film/TheDayTheEarthStoodStill2008 remake made in 2008]] starring Keanu Reeves.
!!This film provides examples of the following:

* AliensStealCable: Klaatu says that his people have been monitoring Earth's radio signals, and that this is the source of his knowledge of Earth culture and language; however, the common subtrope of aliens being unable to distinguish fiction from reality is avoided.
* BenevolentAlienInvasion: Played mostly straight in the original. Subverted in the remake.
* ComicallyMissingThePoint: The two doctors discussing Klaatu's BizarreAlienBiology and superior medical technology unintentionally end up invoking this to modern audiences. After wondering how anyone can live for so long, they end their conversation by casually [[HilariousInHindsight lighting up cigarettes]].
* CoversAlwaysLie: You know that famous poster with Gort holding a woman and firing lasers from his eyes? Yeah, he's not evil.
* CrowdPanic: When the spaceship first lands and when Gort first appears.
* CrushKillDestroy: Averted
* CyberCyclops
* DisintegratorRay: Gort's eye beam
* EarthShatteringKaboom: Klaatu warns that if humanity continues to be so violent, his society will have to do this.
* EinsteinHair: Professor Barnhardt
* TheEndOfTheWorldAsWeKnowIt
* FirstContact
* FlyingSaucer
* FutureMusic
* GenreSavvy: Klaatu, due to his knowledge of Earth culture. When the human officials try to give him lame excuses why he can't meet world leaders and claiming that such meetings are without any precedents, he points out the United Nations exists to do just that.
* GodTest: As a demonstration that he is a powerful alien, Klaatu is asked to stop traffic so a man can cross the street. He does so by cutting power ''all over the globe'' with the exception of hospitals and airplanes in flight.
* HanlonsRazor: For the most part, Klaatu blames human aggression and violence on ''irresponsibility'', not malicious intent.
* HolographicTerminal: The UrExample. Being a movie from the 1950's, Klaatu of course does not have access to CGI hologram special effects, but he does wave at his computer to control it from a distance.
* HumanAliens
* HumanityOnTrial
* HumansAreBastards
* HumansAreMorons
* InnocentAliens
* InterruptedCooldownHug
* JerkAss: Tom, who rats Klaatu out to the Feds.
* KillerRobot
* NiceJobBreakingItHero: The item shot out of Klaatu's hand was a gift for the President that would have advanced science significantly.
* NoCelebritiesWereHarmed: Professor Barnhardt is a clear stand-in for AlbertEinstein.
* PoorCommunicationKills:
** Almost. Klaatu refuses to deliver his message until he can deliver it to representatives of each nation in person, all at once. The 'kills' part comes from the threat of global destruction if everyone doesn't listen. He also never communicates this threat to the appropriate people.
*** He also assumes that walking right up to the military with a strange object that pops open unexpectedly couldn't be misconstrued ''at all''.
** Helen tells Tom not to tell the authorities about Klaatu, but doesn't say why it's such a bad idea - that Klaatu's people will destroy Earth.
* ScareChord: The Piano got some really bad abuse during the making of this film.
* ScienceMarchesOn: There's a news report which casually states the most likely candidates for Klaatu's homeworld are Venus and Mars because they are the most likely planets to be capable of supporting life. In 1951 this would have made sense as it was suspected that Venus could be similar to Earth, and Mars had long been suspected as a possible candidate for life. We now know that the runaway greenhouse effect on Venus makes it too hot to support ''anything'' let alone a species intelligent enough to develop interplanetary travel, and so far there has been no solid evidence of life on Mars and most will agree that if there is anything at all, it probably won't be much more than bacteria. In fact since then scientists have actually been shifting focus even further out towards various Moons among the Jovian bodies (Jupiter, Saturn, Uranus, Neptune) as more likely candidates for extra-terrestrial life.
* ScreamingWoman: Helen
* ShootHimHeHasAWallet: Happens to Klaatu in the beginning.
* SpacePolice
* SpaceWhaleAesop: Give up war or be destroyed by robots from outer space.
* TwoOfYourEarthMinutes: When Klaatu is telling the President's representative how long and how far he's traveled to reach Earth.
* WeComeInPeaceShootToKill: Of the first variety.
** Partial aversion. Almost everyone is (reasonably) suspicious of Klaatu at first, but only one nervous soldier actually shoots him. It's not until Earth Stands Still (a harmless demonstration of power, meant to get Earth to recognize the seriousness of the situation), that everyone starts trying to kill him.
* WhiteAndWhiteMorality
* WorthlessYellowRocks: Klaatu's diamonds.