Captain Blunderpants is the evil counterpart of Captain Underpants. He is from the opposite "Purple Potty" universe. He was defeated by George and Harold's grandparents. When he is Mr. Krupp he is nice. But when he is Captain Blunderpants he is nasty and evil. Contrasting from the Captain Underpants in the regular universe, when water is poured on his head, he becomes Captain Blunderpants, but when someone snaps their fingers he turns back into Mr. Krupp. Also, when Captain Blunderpants is in his bad form he has a toupee, but in his Mr. Krupp form he does not wear a toupee. He is the tertiary antagonist of Captain Underpants and the Preposterous Plight of the Purple Potty People.
Captain Blunderpants is evil and very nasty. But when he is in Mr. Krupp form he is the best principal you would know and he loves everyone and everything. However Evil George and Evil Harold are not amused by his happiness.
Captain Underpants and the Preposterous Plight of the Purple Potty People
Continuing from the previous book, George, Harold, Sulu, and Crackers have ended up in an alternate universe that is an opposite version of their own world. George and Harold discover that Mr. Krupp is nice and does not wear a toupee in this universe. They then see their evil counterpart, Evil George and Evil Harold, and learn through one of their more accurate comics that they had transformed their principal into a villain named Captain Blunderpants, the opposite dimension form of Captain Underpants. Sulu and Crackers are kidnapped by Evil George and Evil Harold and they use the 3D Hypno-Ring to hypnotize them into being evil. Sulu attacks Good George and Good Harold. Crackers, on the other hand, saves them (though George and Harold can't figure out why at this time).
The duo finally get back to their dimension of the multiverse, but unintentionally bring Evil George, Evil Harold, Nice Mr. Krupp (he wanted to pet Crackers), and Sulu with them. As they realized what reality they were in Evil George and Evil Harold get water on Nice Mr. Krupp's head, transforming him into Captain Blunderpants and off they fly into the city to raise chaos.
After Evil Sulu was defeated by Captain Underpants, Evil George and Evil Harold and Captain Blunderpants arrive to the scene.
Captain Blunderpants and Captain Underpants were about to face off against one another in an epic battle but before it could happen, Good George snapped his fingers and Captain Blunderpants became Nice Mr. Krupp. However, the moment is short-lived when it starts to rain and both begin to change as their happiness turns into pure anger and hatred. Captain Underpants comes out of his trance into Nasty Mr. Krupp while Nice Mr. Krupp comes into his trance becoming Captain Blunderpants, again breaking out of the ropes in rage as an angry Mr. Krupp storms off, back to his house dressed as Captain Underpants, not contributing to what is going on around him and assuming it all a dream. Good George and Harold snaps their fingers trying to get Nasty Mr. Krupp to turn back in Captain Underpants and Blunderpants back to Nice Mr. Krupp but due to the rain pouring too hard it is impossible.
Since Captain Underpants is out of commission to take a stand against Blunderpants, George's Grandmother and Harold's Grandfather has to take a stand and they become the two elderly superheroes named Boxer Boy and Granny Girdle, like the ones in Good George and Harold's newest comic book.
Captain Blunderpants is defeated at last by the elderly heroes and is kicked back into his alternate reality along with the evil versions of George and Harold.
However, due to him causing havoc in the City of Piqua in the normal universe along with Evil George Beard and Evil Harold Hutchins, their good counterparts Harold Hutchins, George Beard and Benjamin Krupp (aka Captain Underpants) have been framed and arrested for the crimes that their evil counterparts committed.
- While his opposite sings "Tra-La-Laaaaaaa!", Captain Blunderpants sings "La-La-Traaaaaaaaa!"
- Unlike Captain Underpants who drank super power juice to get stronger and have super powers, two trucks of chocolate and peanut butter collided and crashed on Captain Blunderpants and the two mixtures of Chocolate and Peanut Butter become radioactive, giving him superpowers as revealed in the Evil Treehouse Comic Book Evil George and Evil Harold wrote about which is true in real life in the alternate reality.
- Since Captain Blunderpants is Captain Underpants' evil counterpart, snapping fingers and splashing him in the face with water have opposite effects. Furthermore, Evil George and Evil Harold deliberately cause Nice Mr. Krupp to transform into Captain Blunderpants as opposed to Nasty Mr. Krupp being changed into Captain Underpants by accident at the end of every book.
- Captain Blunderpants and Captain Underpants met each other but never got to face off and battle each other due to Good George taking action by snapping his fingers turning Captain Blunderpants into Nice Mr. Krupp.
- Captain Blunderpants is a parody of Ultraman as he is the opposite of Captain Underpants (who is a parody of Superman) much like Ultraman is the opposite of Superman.
- Nice Mr. Krupp looks similar to his alternate universe counterpart Captain Underpants, but isn't shown to do anything heroic beyond being nice and funny and cheerful and kind to everyone. Captain Blunderpants looks similar to his alternate universe counterpart Nasty Mr. Krupp, when Captain Blunderpants wears the toupee. Both Nasty Mr. Krupp and Captain Blunderpants are both ruthless and evil and petty but Blunderpants is willing to commit criminal activity such as stealing, destroying and causing harm as opposed to Nasty Mr. Krupp simply mistreating children.
- Captain Blunderpants came close to a challenge with Captain Underpants but since Captain Underpants was turned back into Mr Krupp, Granny Girdle and Boxer Boy took and stand and defeated him instead.