Technically The Day the Earth Stood Still (1951) is not an alien invasion film. While aliens are present and do cause mild destruction and mischief; their agenda is never invasion but rather atomic disarmament. The mysterious alien Klaatu gives the human race a choice between abandoning destructive technology or total elimination. That’s pretty heavy subject matter for 1951.
The humanistic story is enhanced by featuring the friendliest, most cordial extraterrestrial prior too E.T. Michael Rennie plays Klaatu like a wise elder statesman; his performance is the greatest reason to see the film.
A robot gives the other great performance in the film. Gort’s vague human features and complete power have been enough to secure is status as a science fiction icon.