The Day The Earth Stood Still (1951)

In Robert Wise's seminal, big budget science-fiction film:

• the film's intriguing title sequence of an extra-terrestrial vessel's approach into the Earth's atmosphere, emphasized by the electronic sounds of theremin theme music
• the initial flying saucer-spaceship landing on the Ellipse in Washington DC in 1951 - causing a panic and troop deployment
• the sequence of the emergence of a humanoid, benevolent, pacifist, interplanetary alien emissary-visitor named Klaatu (Michael Rennie), who was seeking peace - he walked down a ramp, held out his hand, and announced: "We have come to visit you in peace and with good will" - but when he pulled out a device or object from inside his spacesuit (later described as a gift to the US President), an edgy soldier fired his weapon, and the device was shattered in pieces and seen lying on the ground next to the wounded Klaatu
• suddenly, through the hatch of the vessel-ship emerged a silent, killer bodyguard - a giant robot named (Gort); he descended the ramp from the ship and confronted the military force; he had the ability, when threatened, to zap (vaporize or melt) the soldiers' weapons, tanks and giant guns with a lethal, disintegration, death-ray laser beam heat-ray behind his sliding visor; the robot, an interstellar guardian - a member of a police force, also had the power to destroy worlds such as Earth, whose inhabitants were intent on destruction, aggression, and hostility; however, his main objective was to warn Earth to establish peace
• the sequence of Klaatu's (now using the name Mr. Carpenter) tour of Washington DC, led by the son Bobby (Billy Gray) of young WWII war widow Helen Benson (Patricia Neal), including their visit to Arlington Cemetery (and the grave of Bobby's father, who was killed at Anzio) - Klaatu was amazed ("Did all those people die in wars?"); Klaatu was impressed with the Lincoln Memorial (and its inscribed Gettysburg Address)
• Klaatu's meeting with Bobby's recommendation for "the smartest man in the world" -- the Einstein-like scientist character Dr. Barnhardt (Sam Jaffe), who conferred with Klaatu, and was told that other alien peoples threatened to completely eliminate Earth (after its development of atomic power) if they didn't seek peace and heed his message
• later in the film, Gort demonstrated his power one day at noon, by shutting down the world's power supply for 30 minutes (hence, the film's title "The Day the Earth Stood Still")

Gort Menacing Helen Benson Before She Commanded: "Klaatu barada nikto"

• the scene of young WWII war widow Helen Benson (Patricia Neal) menaced outside the spaceship by the shadowy approach of Gort; to save herself, she delivered a command of three words - "Klaatu barada nikto" given to her by Klaatu - to prevent the menacing Gort looming above her from killing her and destroying the planet after Klaatu had been shot (and killed) by troops; afterwards, the robot carried Helen in his arms into the spaceship

Klaatu's Farewell Address

• the film's soft-spoken final scene, with resurrected extra-terrestrial Klaatu's pro-disarmament address to scientists and other top leaders - he lectured and warned world leaders with a final challenge, as robot Gort stood behind him near the entrance to their spaceship - before they departed: ("...but if you threaten to extend your violence, this Earth of yours will be reduced to a burned-out cinder. Your choice is simple. Join us and live in peace or pursue your present course and face obliteration. We shall be waiting for your answer. The decision rests with you")