The Day the Earth Stood Still 1951

An alien (Klaatu) with his mighty robot (Gort) land their spacecraft on Cold War-era Earth just after the end of World War II. They bring an important message to the planet that Klaatu wishes to tell to representatives of all nations. However, communication turns out to be difficult, so, after learning something about the natives, Klaatu decides on an alternative approach. IMDB