Enigma: A narrative device that teases the audience by presenting a puzzle or riddle to be solved.
This is when a mystery is created either relating to the narrative or the character in the story.
Remember the opening sequence from the film "Desperado" when Steve Buscemi talks about the Antonio Banderas character. The sequence cuts between interest created by the story-telling in the bar and the mystery created by the filming techniques used to obscure Banderas' identity.
The camera tilt which classically reveals a characters identity has long been a feature of Hollywood western genre.
Desperado example of Enigma
The actor Clint Eastwood often played the mysterious stranger in the spaghetti westerns he made in the 1960's
Classic example of how enigma is created in film
The Mast of Zorro
The enigma or mystery of characterisations are often used as a seduction devise in films too. A classic example of this was the film "The Graduate".