Jason Voorhees () is a character from the Friday the 13th series. He first appeared in Friday the 13th (1980) as the young son of camp-cook-turned-killer Mrs. Voorhees, in which he was portrayed by Ari Lehman. Created by Victor Miller, with contributions by Ron Kurz, Sean S. Cunningham and Tom Savini, Jason was not originally intended to carry the series as the main antagonist. The character has subsequently been represented in various other media, including novels, video games, comic books, and a crossover film with another iconic horror film character, Freddy Krueger.

The character has primarily been an antagonist in the films, whether by stalking and killing the other characters, or acting as a psychological threat to the protagonist, as in the case of Friday the 13th: A New Beginning. Since Lehman's portrayal, the character has been represented by numerous actors and stuntmen, sometimes by more than one at a time; this has caused some controversy as to who should receive credit for the portrayal. Kane Hodder is the best known of the stuntmen to portray Jason Voorhees, having played the character in four consecutive films.

The character's physical appearance has gone through many transformations, with various special makeup effects artists, including Stan Winston, making their mark on the character's design. Tom Savini's initial design has been the basis for many of the later incarnations. The trademark hockey goalie mask did not appear until Friday the 13th Part III. Since Friday the 13th Part VI: Jason Lives, filmmakers have given Jason superhuman strength, regenerative powers, and near invulnerability. Some interpretations suggest that the audience has empathy for Jason, whose motivation for killing has been cited as being driven by the immoral actions of his victims and his own rage over having drowned as a child. Jason Voorhees has been featured in various humor magazines, referenced in feature films, parodied in television series, and was the inspiration for a horror punk band. Several toy lines have been released based on various versions of the character from the Friday the 13th films. Jason Voorhees's hockey mask is a widely recognized image in popular culture.