In the Friday the 13th film franchise, which film first features Jason Voorhees as the killer?

Friday the 13th Part II is the first film in which Jason Voorhees is the killer.

The 1980 original Friday the 13th reveals that Pamela Voorhees, Jason's mother, is responsible for the murders at Camp Crystal Lake. Jason appears in the film's ending as a child in a brief dream sequence, but he is not the adult killer.

Jason becomes the central murderer in Friday the 13th Part II, released in 1981. In that film he wears a burlap sack over his head rather than the hockey mask that later becomes his signature image. The hockey mask first appears in Friday the 13th Part III.

This distinction is a common franchise mix-up. Jason is the most recognizable figure in the series, but Pamela Voorhees is the killer in the first movie. Later sequels expanded Jason's mythology and repeatedly brought him back after apparent deaths.