Doctor Diaper

"Not so fast!"

- Dr. Diaper

Dr. Diaper (or Dr. Niko Nappy in UK versions of the Captain Underpants books) is the primary antagonist in The Adventures of Captain Underpants, whose plan is to blow up the moon with the Lasermatic 2000. Doing this would result in giant chunks of the moon crashing down on Earth, crushing every major city. This chaos would allow him to take over the planet.

He is voiced by Len Forgione in the Sound-O-Rama Audiobooks.

The Adventures of Captain Underpants
After George Beard and Harold Hutchins were chasing Captain Underpants through Piqua, Dr. Diaper's Robots stole a crystal at a shop for the Lastermatic 2000 to work. They went in a van and Captain Underpants' cape got stuck on the van's door with George and Harold hanging on. They stopped at Dr. Diaper's warehouse and the evil team captured Captain Underpants. Dr. Diaper initiated the Lasermatic 2000 and it would be finished in 20 minutes. George and Harold found some planks in the warehouse and destroyed the robots. Afterward, they shot a piece of fake dog doo-doo at Dr. Diaper's feet. He then thinks he had an accident and goes to change himself. They rescue Captain Underpants and try to find a way to shut the machine off. Harold then finds and pulls the self-destruct lever on the Lasermatic 2000. This turned it off and it soon began to malfunction as it was about to self-destruct. Dr. Diaper then appears out of nowhere and gets angry at this. He points his Diaper-Matic 2000 at our heroes, but Captain Underpants shoots his underwear and it lands on Dr. Diaper's head. After escaping the warehouse as it explodes, our heroes arrive at a police station, but it was closed so they hung Dr. Diaper on a pole nearby and put a note on him so that the cops can arrest him.

Captain Underpants and the Perilous Plot of Professor Poopypants
When Professor Poopypants is sent to jail, Dr. Diaper is shown in the jail that the professor is sent to. He, the other inmates, and two security guards are shown laughing at his silly name.

Captain Underpants and the Preposterous Plight of the Purple Potty People
When George and Harold go in the alternate universe and discover that all of the villans from the past became good, Dr. Diaper is seen as a police officer.

Captain Underpants and the Terrifying Return of Tippy Tinkletrousers
Near the end of the book when Tippy saw the devastated future, the little boy says that some guy in a diaper, presumably Dr. Diaper, blew up the moon and was later eaten by one of the Talking Toilets.

Captain Underpants: The First Epic Movie
He is briefly referenced in the scene where Captain Underpants reads his comics in George and Harold's treehouse.

Trivia

 * He is the only main Captain Underpants enemy so far to not have some sort of origin revealed. He is also the only one who George and Harold were not part of creating at all, other than Sir Stinks-A-Lot.
 * The toilets were brought to life by the PATSY 2000, Zorx, Klax, and Jennifer flew into the school, Tippy Tinkletrousers was annoyed into becoming evil, Wedgie Woman was hypnotized, Carl, Trixie, and Frankenbooger were left with Melvin's evil, Captain Blunderpants, Evil George, and Evil Harold were Captain Underpants, George, and Harold's villainous counterparts, and The Wedgie Magee was made up.
 * He is one of the few villains to still remain alive and in existence. The only other villains to not be killed or removed from existence would be Evil George, Evil Harold, and Captain Blunderpants.