The Day the Earth Stood Still is one of the all time classics of science fiction. Released in 1951 and based on the short story; Farewell to the Master by Harry Bates.
Klaatu the humanoid alien, with Gort his bodyguard robot, come to earth with a warning for humanity. And that's about all you need to know about the plot really. The rest of what it's about is the national paranoia manifest in the post WW II, Cold War era America in which the film is set. And its all very very good so for those that haven't yet had the pleasure it's well worth seeking it out.
And here's some snaps of Klaatu in his space suit.
There's not much more to add really except;
Klaatu barada nikto