The Day The Earth Stood Still is based on a classic
SF short story by
Harry Bates called
Farewell To The Master. It features Klaatu and Gort, but has a slightly different point than the movie.
The kicker, the grand revelation in italics that all 1940's SF was legally required to have, was (get ready, now. Are you sitting down?)
The robot was in charge. In the galactic culture of which they were ambassadors, humans took second place to their creations. Imagine if the filmmakers had tackled this aspect head-on, without the Frankenstein twist that seems to still follow us around.