A good costume from a movie I remember is Darth Vader from Star Wars, directed by George Lucas. The black gas mask creates an intimidating impression with the audience due to the black design showing the audience his evil nature and it as well giving him a robotic and larger than life impression on the audience.

As well the unique design that looks nothing like any of the other costumes in Star Wars help to elevate his significance in the story to those watching. As well a eluding to his powers with the force.

Lastly the costume helps to signify his part in the empire by its pristine look. Since everything associated with the empire in star wars is well designed and clean. His suit having that quality as well as its similarity to a storm trooper suit helps to associate him with them.

Lastly since most of the backgrounds hes in are either grey or white, it has a nice contrast off them