One scene was cut from the movie before it was released. The original script called for Klaatu to be taken to a police station by the government man who came for him at the boarding house, not directly to Barnhart's home. At the station, men were being dragged in from all over and questioned, and Klaatu becomes upset when he sees how a man was beaten up by a crowd because they thought he was the spaceman. The scene was cut because director Robert Wise realized that the audience was interested in the Klaatu/ Barnhart meeting and the scene at the police station was unnecessary, but on the DVD there are stills from that deleted scene.
Originally Klaatu's death and resurrection at the end of the movie was meant to be permanent, reinforcing his God-like powers, but at the time the Breen Office - the film industry's censors - didn't like the ending, suggesting it was too left-wing, and insisted that director Robert Wise and writer Edmund H. North put in the line, "That power is reserved for the Almighty Spirit". Both Wise and North hated the line and thought it completely inappropriate - negating the concept of Klaatu's race being all-knowing and all-powerful - but the studio wouldn't back them up and they were forced to put it in.
Ranked #5 on the American Film Institute's list of the 10 greatest films in the genre "Sci-Fi" in June 2008.
Some reference works state that Adventures of Superman star George Reeves appeared as a television news reporter with eyeglasses in one sequence. This is not true. The actor playing the role bears no resemblance to Reeves, and in a 1995 interview with Reeves biographer Jim Beaver, director Robert Wise stated unequivocally that it is not Reeves in the role. It appears that someone jumped to conclusions based on the image of a reporter wearing glasses and thus resembling roughly the image of Superman alter-ego Clark Kent. Reeves had nothing to do with the film in any capacity.
Speaking of the different versions of Gort's suit, you can see the seam and laces on the front of his suit in the shot where he first starts to carry Helen to the ship.
The Army refused to co-operate after reading the script. The National Guard had no such qualms and gladly offered their co-operation.
The film was shot on the 20th Century-Fox back lot, which is now an upscale office complex known as Century City.
The first actor to whom the role of Klaatu was actually offered was Claude Rains, who wanted to accept it but had to decline because of a prior commitment on Broadway.
The name "Richard Carlson" - another leading sci-fi actor of the 1950s - appears at the bottom of the glass door to Hugh Marlowe's office.
The original choice of actor to play the alien visitor was Spencer Tracy.
The phrase "Klaatu barada nikto" has become a popular phrase among sci-fi fans over the years and has been featured in other movies, such as Army of Darkness.
The role of Gort was played by Lock Martin, the doorman from Grauman's Chinese Theater, because he was extremely tall. However, he was unable to pick up Helen because he was so weak and had to be aided by wires (in shots from the back where he's carrying her, it's actually a lightweight dummy in his arms). He also had difficulty with the heavy Gort suit and could only stay in it for about a half-hour at a time.
The role of Klaatu was originally intended for Claude Rains.
The scene of the large crowd fleeing the saucer area after Gort appears is all too obviously "speeded up" film, making the shot look unnatural. The reason for the sped up film effect was explained by director Robert Wise in an interview - it seems that, despite much pleading and cajoling from him, the crowd of inexperienced extras portraying the saucer onlookers simply wouldn't move away from the saucer quickly enough to look panicky and convincing. After several takes, Wise finally had to move on with filming and reluctantly allowed the scene to be "sped up" in post production, knowing that the end result would probably looked staged.
The screenplay was based on the story "Farewell to the Master" by Harry Bates. It was originally published in the pulp magazine "Astounding Science-Fiction."
The spaceship was made of wood, wire and plaster of Paris.
There were two Gort suits: one that laced up down the back for when he had his front to the camera, another that laced up in the front for the shots of his back.
Three years after this was made, it was adapted for the "Lux Radio Theatre". Michael Rennie and Billy Gray reprised their roles. Jean Peters played the role of Helen.
To depict the seamless closing of the ship and its ramp, they just reversed the film of the shot of the ship's ramp and door appearing.