Zorx, Klax, and Jennifer

"Look at those puny earthlings! They're all drinking Evil Zombie Nerd Milkshakes and transforming before our very eyes!"

- Zorx

"It won't be long now. Tomorrow, we'll feed them Super Evil Rapid-Growth Juice! Then they will grow to the size of Xleqxisfp trees."

- Klax

"Exactly. Then we will unleash our giant evil zombie nerds upon the earth, and soon the planet will be OURS!"

- Jennifer

Zorx, Klax, and Jennifer are three space aliens who planned to invade Piqua, Ohio in Captain Underpants and the Invasion of the Incredibly Naughty Cafeteria Ladies from Outer Space (and the Subsequent Assault of the Equally Evil Lunchroom Zombie Nerds). They put this into plan by infecting the school with Zombie Nerd milkshake. They serve as the primary antagonists of the book.

They are voiced by Len Forgione in the Sound-O-Rama Audiobooks.

Captain Underpants and the Invasion of the Incredibly Naughty Cafeteria Ladies from Outer Space (and the Subsequent Assault of the Equally Evil Lunchroom Zombie Nerds)
They land on top of Jerome Horwitz Elementary School. Later, the lunch ladies at the school quit and the aliens fill in for their spot. They plot to turn the students and faculty at the school into Evil Zombie Nerds using Evil Zombie Nerd Juice. George and Harold are eating lunch in Mr. Krupp's office and walk out and see the problem. George and Harold promptly sneak into the kitchen and pour the Super Evil Rapid Growth Juice outside. They tell Mr. Krupp about the situation, but he doesn't believe them. Ms. Anthrope then walks into his office and takes a huge bite out of his desk.

George, Harold and Mr. Krupp run into the kitchen, and the evil Zorx somehow snaps his tentacle, transforming Mr. Krupp into Captain Underpants. The heroes are trapped by the Zombie Nerds, and they climb up a ladder to the roof. They go into the alien spaceship and see a refrigerator full of juices. They are jailed in the spaceship by the aliens. George and Harold switch the Super Evil Rapid Growth Juice label with the Ultra-Nasty Self-Destruct Juice label, then switch the labels for the fuel tank and spray gun. The space aliens are killed when they pour Ultra-Nasty Self-Destruct Juice in the engines and cause the spaceship to explode.

Captain Underpants and the Preposterous Plight of the Purple Potty People
When George and Harold accidentally enter a backwards universe after using the Purple Potty two days in a row, the two find Zorx, Klax, and Jennifer working as firefighters alongside Professor Pippy P. Poopypants.

Captain Underpants and the Terrifying Re-Turn of Tippy Tinkletrousers
In an alternate reality where Tippy Tinkletrousers accidentally scared Kipper Krupp, which resulted in Mr. Krupp getting fired and not turning into Captain Underpants, the aliens successfully turned all the teachers and students into Giant Zombie Nerds. While the Zombie Nerds are seen, the aliens aren't mentioned. Since the aliens were mentioned in past tense, it's likely that the three were betrayed by the Zombie Nerds and supposedly killed by them.

Captain Underpants: The First Epic Movie
In the fun-fair scene, crudely drawn images of the aliens appear as targets for a carnival game. They also make a cameo in the end credits.