Megaweapon is an armored truck in the film Warrior of the Lost World that was created by the Omegas to enforce their law on the lawless roads of the post-apocalyptic world. The truck has spikes on the front and shoots fire. It was stopped by the Rider by sabotaging the circuitry in the underbelly causing it to short-circuit.
When Warrior of the Lost World was featured on Experiment 501 of Mystery Science Theater 3000, Joel Robinson, Crow T. Robot, and Tom Servo found the Rider to be so unlikeable a character that they cheered for Megaweapon instead. At the episode's end, they called Megaweapon by telephone, and Megaweapon (voice of Michael J. Nelson) revealed "he" had survived apparent destruction in the film and, like the crew, could not remember the name of the actor who played Rider (As a running gag throughout the episode, the actor (Robert Ginty) was referred to by the Joel and the 'Bots only as "the Paper Chase guy." Megaweapon claimed that Ginty's fellow actors used this nickname as well). Megaweapon was occasionally referred to in the riffs of later episodes, such as Episode #614 with San Francisco International.