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Chief Knock-A-Homer looked like an oversized mailbox, with three wheels on the bottom, a viewport in front, flexible arms (with grasping hooks) at the sides, and an Indian war bonnet on top of its head. Chief Knock-A-Homer's primary weapon was a hammer, but it was capable of disarming opponents and using their own weapons against them.
Homer originally tried to make a real robot to enter into the show, but he was unable to make a working robot. Unknown to anyone else, Homer changed his plan and designed Chief Knock-A-Homer for an operator (himself) to be inside it, pedaling a tricycle and putting his own arms into the robot's arms (essentially making them act as sleeves) to do things like swing the hammer. However, because Homer included a remote control, Bart thought that he was controlling the robot. Homer later confessed to Bart that the remote wasn't doing anything except delivering electrical shocks to Homer's butt, which Homer had set up on purpose to help maintain his competitive edge.
Chief Knock-A-Homer defeated many opponents, among them Buzzkill, Ralph-O-Cop and Murderpuss. However, it came up short against Killhammad Aieee, a very high-tech robot entered by Professor Frink and his son. Kilhammad Aieee nearly destroyed Chief Knock-A-Homer, but the fight ended in a draw. Homer was nearly killed in that fight, and was also "outed" as having been inside the robot all along. As it turned out, Bart was more impressed by Homer's being inside Chief Knock-A-Homer and doing all the fighting for real than he had been when he'd thought that Homer had only built the robot.