Excalibur (1981) - Mordred's Gold Helmet (prototype version)
The armor was created by Terry English, and his design for Morderd's armour became the lasting image of the film. Today, whenever the film is mentioned, people seem to remember this particular armour more than anything else. There were only three helmets made for Mordred.
Excalibur remains one of my favourite films. I saw it at 13 and it caused a lasting impression and lifelong fascination with Arthurian legends and Wagner's music.
(pls pardon the clumsy watermark. I need new pictures...)