The Reasonabilists (also known derogatorily as "Zorpies") are members of a cult who follow Zorp the Surveyor, whom they believe will destroy the world. For some time in the 1970s, they took over the city of Pawnee, Indiana, but, as of 2011 were reduced to a small and harmless band of acolytes led by Herb Scaifer. They feature in the Season 4 episode "End of the World".
Every few years, they claim the world is going to end. When the end of the world is near, they hold an all-night vigil in the park. They have said the world is going to end 15 times. Their ceremonies require the playing of flutes, much to the delight of Ron Swanson, who sells them handcrafted instruments. The Zorpies, believing in the impending apocalypse, are happy to pay high prices.
After the unfulfilled doomsday of "End of the World", Herb Scaifer discusses with Leslie his revised prediction for the apocalypse. After finding that the park is booked that day, he quickly revises his prediction to an available date.
The Reasonabilists named themselves so because they believe if people criticize them, it'll seem like they are attacking something reasonable.
Details of the group's beliefs and foundations mirror those of Scientology. Zorp is likely based on the Scientology figure, Xenu, with additional horror elements taken from Lovecraftian horror. Inasmuch as they frequently make unfilled predictions of the end of the world, the Reasonabilists could be considered a parody of any number of religious sects; Harold Camping's 2011 end times prediction was likely the most well-known prediction at the time of the "End of the World"'s airing.
Reasonabalism's holy texts are "Organize It!", an unassuming business organisation guide, and "Organize it! 2: Engage with Zorp" which explores the theory of a 28 foot tall lizard with a volcano for a mouth who controls the universe. Both were written by the group's now-deceased founder, Lou Prozotovich.