The series is set in the year 2000. The show follows the exploits of Little Jimmy Sparks, a 12-year-old boy, who controls Gigantor, a huge flying robot, with a remote control. The robot is made of steel and has a rocket-powered backpack for flight, a pointy nose, eyes that never move, and incredible strength, but no intelligence (although he started to tap his head as if trying to think in one episode). Whoever has the remote control controls Gigantor.
Originally developed as a weapon by Jimmy's father, Gigantor was later reprogrammed to act as a guardian of peace. Jimmy Sparks lives with his uncle Dr. Bob Brilliant on a remote island. Jimmy usually wears shorts and a jacket, carries a firearm and occasionally drives a car. Together, Jimmy and Gigantor battle crime around the world, and clash with the many villains who are always trying to steal or undermine the giant robot.