Gort

Gort is a fictional cyclopian humanoid robot from the 1951 film 'The Day the Earth Stood Still' and it's 2008 remake. The character was based loosely on Gnut, a large green robot from outer space in "Farewell to the Master", a 1940 short story by Harry Bates which was used as the basis for Edmund H. North's screenplay. The design for Gort was done by Harry Bates.

The Day the Earth Stood Still (1951)
Gort was constructed to be part of a galactic police force and accompanied Klaatu as escort on a mission of peace to the planet Earth which had yet to encounter the galactic community. Gort does not speak but observes with his single eye what transpires and maintains a security parameter around Klaatu's saucer. After Klaatu sends a signal to Gort informing him that he is in danger Gort begins using his abilities to rescue Klaatu. He only ceases once Klaatu tells him 'Klaatu barada nikto' (Klaatu is not in danger).