Zorbo was one of the Space Mutants that tried to conquer the Earth. When they arrived at Earth, he relayed to his commanding officer that none of the humans know that they had taken over human bodies to blend in with the populace as part of their plan to develop the ultimate weapon to conquer Earth with. Unbeknownst to them, however, Bart witnessed this plan, and made measures to stop it. Originally, they planned on stealing purple-colored objects as ingredients for their ultimate weapon, but after Bart foiled their attempt, they eventually changed the ingredients to hats from the Springfield Shopping Mall, balloons from Krustyland, exit signs from the Springfield Museum of Natural History, and eventually went as far as to steal radioactive rods from the Springfield Nuclear Power Plant. However, Bart foiled them every time, as well as humans that had presumably been allied with them during this time (Nelson Muntz, Lucille Botzcowski, Sideshow Bob, and Marvin Monroe, respectively). After Bart foiled their final plan, Zorbo and his commanding officer, impressed with Bart's courage and luck, proceeded to reward him with a new addition to Mount Rushmore: A mold of Bart Simpson's face.