The Day the Earth Stood Still (1951 film)

"Klaatu... 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 Human Alien Klaatu lands in Washington DC (in a classic flying saucer) during the Cold War era. The paranoid military shoots him, prompting his 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: "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 hilarious) Plan Nine From Outer Space.

A 2008 remake starred Keanu Reeves in the role of Klaatu; you can see the plot of the remake as recapped by a Bum in this video on Bum Reviews.

The Day The Earth Stood Still provides examples of the following tropes:
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 * Aliens Steal Cable: 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.
 * Benevolent Alien Invasion: Played mostly straight in the original. Subverted in the remake.
 * Crush Kill Destroy: Averted
 * Cyber Cyclops
 * Disintegrator Ray: Gort's eye beam
 * Earthshattering Kaboom: Klaatu warns that if humanity continues to be so violent, his society will have to do this.
 * Einstein Hair: Professor Barnhardt
 * The End of the World As We Know It
 * Executive Meddling: At the end, after Gort, the filmmakers were made to add dialogue specifying that the result was temporary and that.
 * First Contact
 * Flying Saucer
 * Future Music
 * Hanlons Razor: For the most part, Klaatu blames human aggression and violence on irresponsibility, not malicious intent.
 * Holographic Terminal: The Ur Example. 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.
 * Hot Mom: Both versions.
 * Human Aliens
 * Humanity On Trial
 * Humans Are Bastards
 * Humans Are Morons
 * Innocent Aliens
 * Interrupted Cooldown Hug
 * Jerkass: Tom, who rats Klaatu out to the Feds.
 * Klaatu Barada Nikto: The Trope Namer.
 * Killer Robot
 * Nice Job Breaking It Hero: The item shot out of Klaatu's hand was a gift for the President that would have advanced science significantly.
 * No Celebrities Were Harmed: Professor Barnhardt is a clear stand-in for Albert Einstein.
 * Poor Communication Kills:
 * 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.
 * Scare Chord: The Piano got some really bad abuse during the making of this film.
 * Screaming Woman: Helen
 * Shoot Him He Has a Wallet: Happens to Klaatu in the beginning.
 * Space Police
 * Space Whale Aesop: Give up war or be destroyed by robots from outer space.
 * Two of Your Earth Minutes: When Klaatu is telling the President's representative how long and how far he's traveled to reach Earth.
 * We Come in Peace Shoot To Kill: 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.
 * Worthless Yellow Rocks: Klaatu's diamonds.

The following tropes apply specifically to the 2008 remake:

 * Aliens Speaking Mandarin Chinese
 * Aliens Steal Cable: used, but not thoroughly: even though the aliens had been studying the Earth for a while, Klaatu had apparently never heard Bach before.
 * Aliens Are Bastards: The aliens are committing genocide against a sentient race to protect a planet which is in no appreciable danger. Even if we wipe ourselves out life will go on, and CO2 and methane scrubbing bacteria will come in and clean up after us. This is instead of just giving us better technology. They had to get to our level of technology, to get to theirs.
 * Avengers Assemble: Gathering the team.
 * Blue and Orange Morality: Presumably Klaatu's actions aren't as hypocritical to him as they are to us.
 * Broken Aesop: We're destroying the other species on our planet, and aliens think that's bad. Fine. So why does Helen's love for Jacob change Klaatu's mind? A mother's love for a child of her own species, while charming, doesn't really show anything except a desire to perpetuate her species. It'd be more valid if she showed love for an animal, perhaps something completely dissimilar to humans. Instead, The Power of Love conquers all.
 * Another problem is how, in the original, despite the distrust he faces, Klaatu still believes in human goodness, whereas in the remake, Klaatu is as distrustful of humans as they are of him.
 * The Cameo: Gurrak
 * Fun With Acronyms: The US government decides Klaatu's robot buddy is Genetically Organized Robotic Technology--apparently, just having Klaatu say "Gort" at some point wasn't remakey enough.
 * Gory Discretion Shot: We never see anyone getting totally disintegrated by the . The worst we see is a technician get a nosebleed and then fall over dead.
 * Gratuitous Foreign Language: Mandarin Chinese. Keanu Reeves tries really hard, but still doesn't get it quite right.
 * Grey Goo: How GORT was going to wipe out humanity.
 * Inferred Holocaust: Maybe. The period of time without electricity isn't specified. See its entry on the trope page.
 * Knight Templar: Klaatu
 * Lowered Monster Difficulty: for certain values of "monster"
 * No Conservation of Energy: The space ship must have had some nice phlebotinum to decelerate that fast without creating enough waste heat to completely level the UN.
 * Product Placement: So blatant that it's distracting.
 * The Remake
 * Spheroid Dropship: In the place of the classic movie's Flying Saucer.
 * The Swarm: The metal insects that comprise GORT.