An interesting perk that started out as a way to provide some extra fire support in random encounter, Mysterious Stranger evolved into a rare perk that instakills the enemy when attacked in VATS in first person games.
Behind the scenes
The Mysterious Stranger perk was originally designed by Scott Bennie.
The Mysterious Stranger in Fallout 3 and Fallout: New Vegas wears a fedora and overcoat, like the protagonists of 1950s film noir.