In 1983, a high-tech theme park called Delos has three parts: Westworld, Medieval World, and Roman World. It is adult entertainment and is filled with highly realistic humanoid robots. High-paying guests can have any adventure they like, including sex and murder. Peter Martin (Richard Benjamin) and his friend John Blane (James Brolin) visit Westworld. The Gunslinger (Yul Brynner) is programmed to pick fights with guests and die in a shootout. The weapons have sensors to prevent them from shooting warm human beings.

The technicians notice problems cropping up, spreading through the park like a virus. The androids in Roman World and Medieval World begin disobeying orders. After enjoying a night with a robot hooker, Blane is accosted by the gunslinger and Martin shoots the robot dead. Held for murder, Martin breaks out of jail with Blane’s help, and they head out of town. A robot rattlesnake bites Blane, and a female robot (Anne Randall) refuses a guest’s advances in Medieval World. When the Black Knight (Michael Mikler) kills a guest in a sword fight, the supervisors try to shut down the park, but are locked in the control room.

Martin and Blane, recovering from a bar-room brawl, wake up in the Westworld brothel. The Gunslinger challenges them to a showdown and Blane is shot dead for real. Martin runs for his life and the implacable Gunslinger follows.

Martin runs through other areas of the park, finding dead guests and damaged robots. A terrified technician (Steve Franken) is shot dead by the Gunslinger. Martin climbs down a manhole and finds the technicians suffocated in the control room. The Gunslinger continues to stalk him into an android-repair lab. Martin throws acid in the Gunslinger’s face, damaging his sensors. With his optical inputs damaged, the robot tracks him by body-heat. Martin hides near a torch and then uses the torch to set the android on fire. Burned to a shell, it continues to follow him until it succumbs to its damage.

The film was written and directed by Michael Crichton, his first. Reviews were mostly positive, particularly praising Yul Brynner’s creepy and implacable android. There followed a movie sequel, a short-lived TV series, and a highly praised 2016 series produced by J.J. Abrams on HBO. The original movie was produced by Paul N. Lazarus III. Every studio turned it down but MGM, which had a reputation for treating scripts in a cavalier manner, but Crichton and Lazarus were treated relatively well. Brynner’s Gunslinger was based on his character Chris Adams in The Magnificent Seven and wore the same clothes. He only charged $75,000 because he needed the money.

This was the first film to use digital image processing, and the first time the term computer virus was used. It was MGM’s biggest earner that year and kept making money. Pretty much the same plot re-appeared in Crichton’s Jurassic Park. Majel Barrett played the Madame of the Westworld brothel. John Carpenter based the indestructible Michael Myers in Halloween (1978) on Yul Brynner’s Gunslinger, and Arnold Schwarzenegger did the same for the Terminator (1984). Yul Brynner’s eye was injured by a blank cartridge. James Brolin was actually bitten by a milked rattlesnake. The Western set was used in Blazing Saddles.