(via PEPLUM TV: SPFX DEPT.)
The Cyclops from THE GIANTS OF THESSALY (1960)
Special effects by Carlo Rambaldi. The cyclops in this movie is pretty good and terrifying. It’s a man in a costume with an animatronic head. The eye and mouth are moving, not stiff (below). Carlo would later work on KING KONG (1976) and ET - THE EXTRA TERRESTRIAL (1982).
Will have to track this down and check it out, if only for this cyclops.