The movie that made Johnny Five a star. As is often the case with 80s computer movies, there is a Cold War theme here, as scientists Steve Guttenberg and Fisher Stevens create a bunch of robots, though they want to use them for good, rather than violent, ends.
Number 5 gets a power surge during a thunderstorm, and develops a personality. He's taken in by kindly Stephanie (Ally Sheedy), but as is also often the case in 80s computer movies, the military are keen to get their hands on him.
It was followed by a poor sequel in 1988, and there have been persistent rumours of a prequel or a reboot which have amounted to nothing solid. If it's warm nostalgic charm you're after though, you've got to go for the original.