 The sibling aliens Kang and Kodos first appeared on the show on this episode . Every Treehouse of Horror episode since this one must have Kang and Kodos as characters , states an unofficial Simpsons rule . Despite this rule , the writers say the duo will often be forgotten and then added at the last second , leading to brief appearances . The idea of Kang and Kodos came from Kogen and Wolodarsky . In the script , Kang and Kodos were shown as " an octopus in a space helmet with a trail of goo " . The finished design was based on the cover of an EC Comics issue . Although originally designed to constantly drool , Groening suggested that they not drool all the time to make the animation process easier . However , the animators did not mind the work , leading to the drooling staying in the script . Kang and Kodos 's names are derived from two Star Trek characters . Kang was a Klingon captain portrayed by actor Michael Ansara in the episode " Day of the Dove " , whereas Kodos the Executioner was a human villain from " The Conscience of the King " . Harry Shearer voices Kang , and Dan Castellaneta voices Kodos . 
