King Pistachion was the king of a species of living pistachio plants known as "Pistachions" from the year 2175. His birth began in the episode "The Substitute" when Milo accidentally created a sentient blob by pouring futuristic pistachio fertilizer owned by Vinnie Dakota and Balthazar Cavendish instead of chemical absorbent on Zack's diomeno hexane spill. Milo had destroyed most of it while some of it was released from the school's vents. The part that flowed through the vents would crawl toward the pistachio seedling that Cavendish stepped on and fix it. Then the tiny plant would start to glow red, igniting a race of living pistachio plants ("Pistachions").
Only one of his Pistachions is briefly seen in the episode "The Llama Incident" during a football game.
- He is the first villain to appear in the series.