The Day the Earth Stood Still (1951) Directed by Robert Wise

Based on short story "Farewell to the master" this early sci fi 50 classic sets the high bar for films even made today. The music is one of the first time the theremin was used in science fiction and it has become synonymous with the genre ever since. Filmed in a pseudo documentary style and using actual reporters  know to the public, the film has a certain realism to it lets say lacking on other futuristic films from the later 50s. 

Spoilers:

The story is not complicated. One day a spaceship lands, in effect, on the White House lawn and a human-like being gets out. He is immediately shot. As he struggles on ground bleeding the gathered crowds suddenly notices a giant humanoid robot has exited the craft and it destroys all the gun and weapons in sight until the injured alien tells it to stop.

In hospital, the visitor, named Klaatu tried to get a meeting with world leaders so he can transmit a serious message to the people of Earth. When made clear this is not going to happen, he escapes to learn about the people by living among them for a while. This causes hysteria and conspiracy theories. He decides to meet a famous Einstein-like scientist to see if he can talk at least to the scientist of Earth and to convince them he agrees on a display of power that won't hurt anyone but will basically scare the crap out of everyone. By stopping all activity on the planet for 30 minutes, the scientists gather to meet him at the spaceship. Sadly this action also increases the pressure to capture him and he is killed trying to escape from the authorities. Before dying he tells a woman he has befriended to go to the ship and say a phrase to Gort, the robot which tells it to get him and bring him back to the spaceship. 

Inside the ship, Gort revives Klaatu and he leaves the ship to give an ultimatum to all the humans on Earth. Keep your weapons and violence on your own planet or Gort and other like him, who keep the peace between planets, will return and destroy the Earth to "a burnt out cinder".

This is a classic for a million reasons. The effects are sparse but very effective and still look good, the performances are very good and the actors, especially Rennie take their roles seriously and the message of peace, or else is pretty effective. 

Klaatu lives in boarding house while trying to get a feeling for your everyday human and there he meets a single mother and her son. The father was killed in the war and her new suitor is determined to marry as soon as they can. Billy Gray is the child actor and for once, it's role that doesn't grind the film to a halt. Patrica Neal is amazing as the mom who is career oriented, smart and one of two people Klaatu trusts. There is a good rapport between them and it never gets romantic, something that would have seriously undermined the film. When she is stuck in an elevator with him during the world-wide shutdown and he tells her who he is why he is there (which we don't see happen) she is shook to her core and we get how badly this meeting or worlds could go. Her boyfriend, on the other hand sees only ways to become known and make money off Klaatu's real identity and she dumps him without regret. 

Micheal Rennie is perfect. Unknown at the time his performance is a mix of superiority, confusion and bemusement as he tries to navigate human society. He has no patience for foolishness but his goal is to warn not punish humankind... Gort will do that if needed. I love the scene where he asks for a flashlight and can't figure out how it works and when the child shows him his look says "How cute! A switch!". its endearing but also character-wise shows he really doesn't come from around here. When he takes the boy to Arlington Cemetery to visit the father's grave he is touched and it manages to relay how dying in a war is completely, for lack of a better word, alien to him. 

The restored Blu-ray is worth buying. Though there are a few nonsensical things in the movie (only 2 guards for the spaceship at night? How does Gort walk from the ship to where Klaatu's body is with no one noticing an 8 foot alien robot on the streets?) there is only one shot that takes me out of the story. When Gort is seen by the crowd they run away... sort of. The film is sped up and it looks cartoonish. Apparently the untrained extras just couldn't get it right and Wise had to resort to the film trick or not get the shot at all. 

Gort, Klaatu Barrada Nicto!