Protagonist Number 5 (voiced by Tim Blaney) is one of five anthropomorphic prototype robots proposed for Cold War use by the U.S. military, whereof the inventors Newton Graham Crosby, Ph.D. (Steve Guttenberg) and Ben Jabituya (Fisher Stevens), are more interested in peaceful uses including music and social aid. After a demonstration on the grounds of the developer's company, Nova Laboratories in Damon, Washington, a power surge causes malfunction in Number 5, who later wanders away, barely able to communicate and uncertain of its directive; later to encounter animal-lover Stephanie Speck (Ally Sheedy) in Astoria, Oregon, a young woman maltreated by her ex-boyfriend Frank. Stephanie, initially mistaking the robot for an extraterrestrial visitor, satisfies (through books and television) his demand for 'input', and thus supplies the source-material of a lively, whimsical personality.  This film was conceived after the producers distributed an educational video about a robot to various colleges. Studying other films with a prominent robot cast in them (like the Star Wars series) for inspiration, they decided to question human reactions to a 'living' robot, on premise that none would initially believe its sentience.

Number 5 was designed by Syd Mead, the "visual futurist" famous for his work on Blade Runner and Tron.  Most of the arm movements of Number 5 were controlled by a "telemetry suit", carried on the puppeteer's upper torso. Each joint in the suit had a separate sensor, allowing the puppeteer's arm and hand movements to be transferred directly to the machine. He was also voiced in real-time by his puppeteer, the director believing that it provided for a more realistic interaction between the robot and the other actors than putting in his voice in post-production, although a few of his lines were re-dubbed later.  In April 2008, Variety reported that Dimension Films had acquired the rights to remake the original film.