Characters / Captain Underpants — Villains of the CU Universe

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A collection of villains, monsters, and other mega-maniacal weirdos that our heroes often face in their daily adventures.

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Major Antagonists

Melvin Sneedly

Grade-A Suck Up

^{Click here to see him as "The Bionic Booger Boy"}

Voiced in English by: Jordan Peele (movie), Jorge Diaz (animated series)
Voiced in Latin American Spanish by: Eduardo Garza
Voiced in Japanese by: Kengo Takanashi
Voiced in Hungarian by: Csongor Szalay
Voiced in Norwegian by: Erik Skøld

George and Harold's brainy classmate, he first appeared in book 2 and as a background character in later books, before he became more integral to the plot (and Took a Level in Jerkass to boot).

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• The Ace: The smartest student in Jerome Horwitz Elementary school.
• Adaptational Heroism: In the animated series, he actually redeems himself in the finale of season 2. This never happens in the movie or books.
• Adaptational Villainy: In the books, he did end up becoming a superhero in 11 and saving the heroes in book 10 albeit for self-serving purposes. In the movie, he's more than willing to join Professor Poopypants's evil plan for the sake of extra credit.
• Aesop Amnesia: In the series: every time he learns to be nicer to his classmates, it goes out the window by his next appearance.
• Arch-Enemy: He hates George and Harold as much as Mr. Krupp, if not more, because of their pranks constantly disrupting his need to uphold the rules. In fact, Book 6 has him fantasizing about making them his personal slaves.
• Attack of the 50-Foot Whatever: After an incident in a tissue factory, Melvin turns into a giant, rampaging, robotic booger monster in the last act of Book 6.
  • In the first half of the season 2 finale, the nanobots inside Melvin go haywire resulting in the nerd becoming an enraged giant.
• Bad People Abuse Animals: He tries to spank his pet hamster Sulu with a ping-pong paddle for not obeying his orders. Since he has just used a fusion machine to combine Sulu with a robot hamster and given him super strength, this ends badly.
  • This carries on in the animated series as well. For a science project, Melvin is given a hyper-intelligent chimp named 'Edwin' whom he trains to perform various intelligence themed challenges without properly rewarding him for his efforts. This bites him in the butt at the end where Edwin forfeits the first place ribbon Melvin won and gives it to George and Harold for their own project. And earlier Edwin did attack him after being fed up with Melvin teasing him with the promise of ice cream.
  • In the season 3 finale, he imprisons a wild ocelot named Sebastian and carries him around in a tiny cage. Subverted as he did care about Sebastian enough to break into tears when he flies away.
  • In the Epic Choice-O-Rama special, his latest invention (The Rejuvigator) is made out of a living alligator.
• Being Good Sucks: In Book 11, he can become the Arrogant Hero: Big Melvin and wins Piqua's admiration after he saves them from the destructive Turbo Toilet 2000. However, Melvin decides that being a superhero sucks since he constantly has to drop anything he's doing to help the public with whatever task they have for him no matter how trivial or stupid it may be.
• Berserk Button: As the Bionic Booger Boy, he's still mostly the normal Melvin up until tissues are mentioned. Things quickly went downhill from there.
• Big Bad Duumvirate: While normally The Dragon, he serves this role with his future counterpart in season 2 and the Halloween special with Mr. Krupp before he reforms in both.
• Butt-Monkey: Gets put through a Humiliation Conga in Book 6 by George and Harold out of a Revenge by Proxy for what he did to them. Even besides that, he tends to be on the receiving end of George and Harold's pranks.
• Cassandra Truth: In Captain Underpants and the Attack of the Talking Toilets, he shows George and Harold his newest invention, the Photo-Atomic Trans-Somgobulating Yectofantriplutoniczanziptomiser (PATSY 2000), which can convert 2D images into living beings, and demonstrates by using it to turn a photo of a mouse into a real mouse. They don't believe him and think that it's just a regular photocopier that he put a real mouse into so he could trick them. Lo and behold, when they use the "photocopier" to try and print copies of their newest comic book about Captain Underpants and the Talking Toilets, it ends up creating an army of evil Talking Toilets and the Turbo Toilet 2000. Oh, Crap!.
• Character Catchphrase:
  • "You're so immature."
  • In George and Harold's comics, he has a couple: "I'm telling", and "I'm a dumb nerd".
  • The movie has him saying, "I don't get it." whenever a joke occurs that the other kids find funny in which he does not.
• Child Prodigy: Vastly intelligent despite his elementary school age, and seemingly smarter than his parents.
• The Comically Serious: He's quite humorless and rigid but he's a Laughably Evil character.
• Conforming OOC Moment: Melvin is the school's biggest Teacher'sPet, but in Book 5, he cheers along with the other students when Ms. Ribble announces that she's retiring.
• Cursed with Awesome: He's initially displeased over turning into the Bionic Booger Boy, but finds there are actually benefits to his new form, such as having his own water fountain because no one wanted to user a water fountain that his snot dripped all over it.
• A Day in the Limelight: Book 6 and 7 centers around him.
• Disproportionate Retribution: In Season 3's "The Confounding Concoction of the Crooked Combotato", the boys try to have Gooch disguise himself as Melvin so he can pass his portion of an exercise course. Feeling 'betrayed' by this act, Melvin decides to create clones of the kids except they'll be more loyal and worship him.
• Ditzy Genius: As impossibly smart as he is, he wasn't able to tell Mr. Krupp wore a toupee over his bald head. George sarcastically states he thought Melvin was supposed to be gifted. He also always falls for the signs that George and Harold change around, including one that told him to wash his hands in the toilet.
• Dork in a Sweater: In the film, he sports a sweater vest over his school short.
• The Dragon: Frequently to Mr. Krupp whenever he's at odds with George and Harold.
  • In the final book, it was revealed that he was sent by Mr. Meaner/Sir Stinks-A-Lot to defeat George and Harold.
  • He serves this role to not only Mr. Krupp in the movie, but Professor Poopypants.
  • In the animated series, he’s served this role to at least three people so far! Most of the time, it’s Mr. Krupp, like always. Then in episode 10, he served like this to Ted Murdsley, and then at the end of the Season 1 finale, becomes this to his own future self!
• Dude in Distress: In season 4 episode 2, he ends up becoming the prisoner of the Biglyans. Although he manages to trick them into making him their king in episode 5.
• Enemy Mine: In the season 2 finale, after learning that George and Harold aren't interested in Elitenati Academy and only want to go to summer camp, Melvin decides to stop antagonizing them for the rest of the finale and helps them defeat the out of control nanobots along with his future self even pulling off a Heel–Face Turn by saving the heroes from the nanobot's husk.
• Everyone Has Standards: Despite his constant sucking up to the teachers, even he looked less than pleased when Mr. Krupp and Ms. Ribble were announced to be getting married in Book 5.
  • In the Season 2 finale, he is horrified when his future self plans to betray George and Harold (after they just saved the day, no less) and basically leave them to die.
• Even Bad Men Love Their Mamas: He does love his parents and gets happy to see them in book 7 safe.
• Evil Redhead: Almost every major appearance of his has him playing an antagonistic role, and every colored portrayal of him has drawn him with red hair.
• Flowery Insults: In the animated series, after he vows to "Step up his trash talk" in "The Costly Conundrum of the Calamitous Claylossus", he uses a variety of creative insults whenever he's speaking to the boys, his peers, or even Krupp.
• Foil: To George. While both are The Aces and Child Prodigies of Jerome Horwitz Elementary, George is a Brilliant, but Lazy Nice Guy who likes to spread joy around the school via comics and pranks (in the film and animated series), while Melvin is the Academic Alpha Bitch who's a Gadgeteer Genius and an Insufferable Genius who likes to snitch on anyone, especially George and Harold.
• "Freaky Friday" Flip: In the aftermath of Book 6, the process that de-boogers he accidentally swaps his brain with that of Mr. Krupp, whom he had previously Swallowed Whole while on his rampage.
• Freudian Excuse: It's implied that the reason why Melvin likes to kiss up to his teachers and authority figures at his elementary school is that his own parents don't pay much attention to him at home. So him getting close to the adults at his school is probably him trying to find a replacement parental figure.
  • In the Halloween Special, the reason he despises Halloween so much is that he never got to go trick-or-treating as he always stayed at home giving candy to other kids, such as George and Harold. It also doesn't help that every year the boys would always scare Melvin with their costumes.
• The Friend Nobody Likes: Melvin is unpopular due to his condescending nature and for being an annoying tattletale as well as a buzzkill. It also doesn’t help that his inventions cause the problem of the episode on several occasions.
• Fusion Dance: Book 6 has him deciding to combine himself with a Killer Robot. Unfortunately for him, he accidentally sneezes at the last second, adding his boogers to the mix and turning himself into the Bionic Booger Boy.
• Glory Hound: He really enjoys having Captain Underpants' powers and being seen as the hero.
• Hated by All: While he won't acknowledge it, he isn't very well-liked by his peers given his arrogance and tendency to mistreat them with his ambitions. As shown in season 4 episode 5, the M.I.S.F.A.R.T.S. were only willing to rescue him for the sake of the adventure rather than actually caring about him.
• Heel–Face Revolving Door: Becomes good at the end of season 2. Then becomes bad again in season 3. Then became good again in the Halloween special. And then becomes bad in the Epic Choice-O-Rama special and The Epic Tales of Captain Underpants in Space!. And then becomes good again in the Mega-Blismass Christmas special.
• Hidden Depths: Season 3 Episode 2 shows that Melvin considers the keytar to be an admirable instrument. And in the next episode, he states that he has the same blood type as Stanley and Dressy.
  • The second episode of Season 4 reveals that he is surprisingly skilled at rapping, and has a love of video games.
• Horrible Judge of Character: In the movie. He sucks up to and helps Professor Poopypants with his plan to eliminate laughter, even though the man is clearly insane!
• Hulk Speak: In his Bionic Booger Boy form, after he finds out about the field trip.
• I Just Want to Have Friends: Double Subverted in the animated series. Most of the time, he just treats everyone as his inferiors and claims that he doesn’t need anyone, but a handful of moments in Season 3 (especially episode 1) and the Halloween Special heavily hint that deep down, he is a very lonely kid.
• Impossible Genius: His inventions are not only advanced but sometimes scientifically impossible (though given what series he's in, the laws of physics and science probably only apply slightly more than they do in a Bugs Bunny cartoon). He can effortlessly create killer robots, a photocopier that turns 2D images into living beings, a fusion machine, a separation machine, a memory-wiping machine, and a time machine (which apparently was easy to build). And he's in the fourth grade.
• Insane Troll Logic: In the Halloween Special, his presentation to the Piqua public on why they should cancel Halloween states that everyone will be forced to work in (nonexistent) candy mines to keep up the holiday tradition.
• Insufferable Genius: He was based on an annoying nerd that Dav Pilkey knew back in middle school (given the pseudonym “Michael Sneedman”), who would always rub his perfect grades in the faces of the other kids and would go as far as to grade his own test papers and write “100%”, “A+”, and “Keep up the great work, Michael!” on them.
• It's All About Me: A selfish nerd who only cares about himself and considers everyone around him to be inferior to him. This is exaggerated in season 2 when his future self takes over the school and transforms Jerome Horwitz into his present self's personal devil's Paradise.
• Jerkass: He has his legitimate points, but he can be a completely pompous and condescending snob.
• Jerkass Has a Point: While he went about it in his typical obnoxious way, Melvin was pretty justified in snitching on George and Harold for ruining the science fair in book 2.
  • In season 3 of the animated series he was not wrong when he told the parents Krupp was lying but George and Harold's stupidity causes them to not listen.
• Jerk with a Heart of Gold: Occasionally in the animated series. While his temporary cooperation with George and Harold is usually to benefit himself, Hack-A-Ween is the exception, where he helps them purely because he appreciates for inviting him to celebrate the holiday with them. And even before in the season 2 finale, he refused to abandon the two in Krupp's brain, indicating that despite his usual selfish reasons for teaming up with the protagonists, it's not always the case.
• Laser-Guided Karma: He does become a victim of this often. In Book 7, for selfishly putting himself over the fate of the planet, he gets misblamed for the things that Captain Underpants did in his body & gets chased by an angry mob.
• Mistreatment-Induced Betrayal: In the Season 3 premiere, after overhearing George and Harold talk bad about him and his comic, Melvin decides to undo his Heel–Face Turn and tattles on them to Mr. Krupp to separate them again. Though he turns good again later on.
• Morphic Resonance: When he became the Bionic Booger Boy, he retained his bow tie, glasses, and basic head shape. Justified because the machine combined all three elements, so it makes sense some of his features would be included. Plus, you can see that Melvin actually built a bionic bow tie onto the robot.
• Mugging the Monster: In book 11, he angrily shouts at the Turbo Toilet 2000 to be quiet. Cue the Turbo Toilet 2000 chasing after Melvin.
• Mundane Fantastic: Building things like a Combine-O-Tron or the hypothetical separating counterpart would take about six months to finish, but he can build other things like a robot, a time machine, or a PATSY in under an hour.
• Mundane Utility: Became this to Piqua after becoming Big Melvin. It originally started with reasonable emergencies, only to dwindle to outright petty things such as beating hard levels on video games to fishing wallets out of toilets. He snaps after someone calls ou† for him to ask if her pants make her butt look big, which he discovered after prematurely canceling an experiment which resulted in destroying his bedroom at several months of progress.
• Nerd Glasses: He's the school nerd, so it's expected that he would have glasses.
• Nerdy Bully: Essentially his character, constantly making fun of George and Harold.
• Never My Fault: In "The Confounding Concoction of the Crooked Combatato", he blames George for the creation of the titular monster, even though he was technically the one who accidentally threw the potato into the altered phone booth.
• Nobody Likes a Tattletale: Melvin is hated by most of the students for being a notorious snitch (as well as for being a rude egomaniac). In "Captain Underpants and the Attack of the Talking Toilets", he is stuck Writing Lines on the chalkboard with the other teachers for ratting on George and Harold for ruining the Invention Convention, and he has to write, "I will not be a tattletale."
• No Sense of Humor: As mentioned above, he is the only one who doesn't get the joke whenever the other kids find something funny. In the movie, this is because his brain lacks a "Haha-Guffaw-Chucklotamus", the part of a child's brain that controls the ability to laugh. Professor Poopypants uses him as a tool to wipe out the kids' happiness and joy.
  • Subverted in the animated series. It's not that he has no sense of humor, it's that he has a dull sense of humor. According to him, videos of rotting food are "can't miss comedy".
• Not So Above It All: In Book 4, he is seen laughing with all the other fourth graders when Professor Poopypants introduces himself to the class.
  • Also in Book 7, despite his constant insistence that he's more mature than his peers, he still refers to his mother as "Mommy".
• One-Winged Angel: Bionic Booger Boy is this.
• Parents as People: Melvin's parents are shown to be too busy to spend time with their son. Melvin does, however, still love them. This is one of his redeeming qualities.
• Plot Allergy: In Book 6. Even though it’s only briefly mentioned, it’s his allergy to his family’s cat, Danderella, that causes him to sneeze when attempting to use his Combine-O-Tron 2000 on himself, turning him into the Bionic Booger Boy.
  • In the Halloween Special, he claims to be candy intolerant which is one of the reasons why he hates the holiday so much. In the end, after the boys make peace with him, Melvin admits that he was lying and that he actually enjoys candy. Until he starts to have a negative reaction after eating a piece.
• Redheads Are Uncool: Has red hair and is one of the nerdiest kids in school.
• Remember the New Guy?: When he appeared for the first time in book 2, it was made clear that, despite him not being mentioned in book one, he, George, and Harold all already knew each other.
• The Rival: Comes off as this to George & Harold.
• Skewed Priorities: In Book 7, when he steals Captain Underpants' superpowers, he refuses to fight the Booger Bots due to the childish concern of his depiction in George & Harold's comics. Unless the boys change how Melvin is depicted, Melvin would leave the world to die.
  • In the movie, there's a moment where he actually has a hard time choosing between getting extra credit and surviving.
• Small Role, Big Impact: In book 2, he himself doesn't really do much but tattle on George and Harold, but it was his invention that caused the creation of the Talking Toilets.
• Spoiled Brat: Not as much as Jessica, he has shades of this at times.
• The Stool Pigeon: Melvin is also known to be a snitch.
  • He is usually the Petty Peter or the Snobby Simon depending on the book. He was the Concerned Corey (along with the Snobby Simon because while justified, he still enjoyed seeing George and Harold get into trouble) in book 2 when George and Harold sabotaged a science fair out of spite because they were not allowed to participate.
  • In the movie, he even invents a device called the "Tattle Turtle 200," which exposed George and Harold for causing his Turbo Toilet 2000 invention to malfunction.
• Suddenly Speaking: Happens with the alternate timeline version of him in the animated series, where Mr. Krupp is a mean businessman who used their classmates as unpaid sweatshop workers instead of a mean principle. He also used Melvin as a silent right-hand, but he later begins speaking when he explains how Krupp had been using him as furniture instead of rewarding him for being his servant. He also offers to help the kids escape to freedom, or so he says.
• Talking the Monster to Death: Gives one to his future self as the Season Two finale ends.
• Teacher's Pet: In addition to being this, he's also a huge tattletale. Unsurprisingly, all of the teachers and the principal in the school love him.
• Took a Level in Jerkass: Oh yeah. He wasn't wholly unlikable in Book 2 and him breaking his deal with George and Harold was somewhat justified. Fast forward to book 7 and he's a complete jerkass when he finds out, whilst trapped in Mr. Krupp's body, about Captain Underpants' real identity and blackmails George and Harold in transferring his powers into him. Once he does manage to steal the Captain's superpowers, he refuses to help fight the Booger Bots unless George and Harold changed the comic to have him defeating Captain Underpants.
• Took a Level in Kindness: In the animated series. He went from being willing to kill George and Harold in season 1 to being unwilling to betray them and leave them to die in the season 2 finale. This is downplayed, however, since he stretches that he still doesn't like them and his act of kindness was a one-time thing.
• Unexplained Recovery: In episode 2 of Season 3, Melvin's intelligence is reduced to that of a common animal, and runs off into the forest. In the next episode, he turns up perfectly normal with no explanation.
• Villainous Crush: Has one on Erica Wang in the animated series. But given his reputation, it's highly unlikely that she reciprocates it.
• Villain: Exit, Stage Left: Played straight in the season 3 finale. After his group of supervillains are defeated by the heroes, George and Harold use his device against him by having him dress up as a baby. He leaves the stage in tears as the viewing audience laughs at him.
• Villain Protagonist: The chapters preceding his Bionic Booger Boy transformation are told from his perspective.
• Villain Team-Up: He often teams up with Mr. Krupp to either take revenge on George and Harold or to accomplish a personal and sinister goal.
• When All You Have Is a Hammer…: Especially in the animated series, he tends to jump to using his Impossible Genius skills to solve any problem he encounters, regardless of the amount of overkill.
• Wounded Gazelle Gambit: In episode 12 of Season 3, he pretends to be an unfortunate victim for all the visiting parents to convince them that Krupp is lying to them about how great the summer camp was. It's not like he was wrong in that regard.
• You Wouldn't Like Me When I'm Angry!: He tells Mr. Snoddy this when Mr. Snoddy keeps throwing tissues at him. Although he ends up actually saying "YOU NO LIKE ME WHEN I ANGRY".

Professor Pippy P. Poopypants/Tippy Tinkletrousers

God help you if you make fun of his name.

Voiced in English by: Nick Kroll
Voiced in Latin American Spanish by: Enrique Cervantes
Voiced in Japanese by: Hiroshi Iwasaki
Voiced in Norwegian by: Anders Sundstedt

A brilliant scientist from New Swissland who turned to villainy after being made fun of because of his ridiculous name one too many times by the world and children of all ages. He is a recurring villain that the boys and Captain Underpants have to face on various occasions.

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• Adaptation Name Change: Renamed "Pee Pee Diarrheastein Poopypants Esquire" in the movie. Props to the creators of the film for taking a name like "Professor Poopypants," and somehow making it so much worse.
• Adaptational Villainy: Zig-zagged. In the movie, he isn't driven to craziness from George and Harold's tricks, and is already a villain to begin with. His backstory reveals he'd already snapped when the presenters at the Nobel prize ceremony were too busy laughing at his name to give him his well-deserved award. However, his overall scope is smaller with him aiming to get rid of laughter (even refusing to get rid of the part of the brain that causes laughter due to humans needing it to survive) compared to his book counterpart attempting omnicide by trying to destroy the galaxy, and he doesn't attempt to kill George and Harold and settles on shrinking them instead.
• Affably Evil: In the movie, he's quite cheery as far as mad scientists go, even if he wants to wipe laughter off the face of the planet. Until you make fun of his name...
• Alas, Poor Villain: Sympathy for him may vary since he does lose sight of his goal (as well as his sanity) as the books go on. But when it all comes down to it, he was a legitimately brilliant man with actual qualifications. Heck, he designed a shrink ray and a growth ray to get rid of the world's garbage problems (by shrinking it to nothingness) and solve world hunger (by making all the food super-sized). All he originally wanted was to teach people about science, only for them to not give two shits because he had a funny-sounding name. Even George and Harold themselves had to admit that his villain origins could have been avoided if they didn't make fun of him. Even Word of God stated it was a sad scene if only because oh how long he's been around.
• Alliterative Name: Pippy Pee Pee Poopypants, and later Tippy Tinkletrousers.
• As Long as It Sounds Foreign: Hails from the country of New Swissland, where everybody has ridiculous names.
• Bag of Holding: In The Movie, he pulls out an ax, a chainsaw, and a bundle of dynamite from his tiny briefcase before getting to his resume.
• Been There, Shaped History: His meddling with time was what inadvertently wiped out the dinosaurs, caused the Ice Age, and creates the Big Bang that started the universe.
• Berserk Button: He doesn't take people making fun of his name very well, as the whole of Jerome Horvitz learned the hard way. In the movie, the woman presenting Nobel Prizes learned this much earlier.
  • In the movie, he doesn't like children laughing to the point that it becomes part of his Evil Plan to stop kids from laughing forever.
• Big Bad: Of Book 4, 9, and 10 and in The Movie.
• Breakout Villain: He's clearly the most popular villain in the series, appearing in multiple books and serving as the main antagonist in The Movie.
• Butt-Monkey: Constantly made fun of in his debut. He's also a Butt-Monkey in the movie.
• Card-Carrying Villain: He doesn't even try to be subtle in the movie. Captain Underpants has a good feeling about him anyway.
• Chronic Backstabbing Disorder: During his reappearance, he abuses time-travel twice to solve his problems, creating "clones" of himself. All three clones betray the others at the first opportunity. When Harold and George are arguing about how to get home, one of them points out that they can't trust him, since he can't trust himself.
• Comically Missing the Point: At the end of Book 4, he decides to take George and Harold's advice to change his name so people won't laugh at him anymore. He decides to rename himself "Tippy Tinkletrousers".
• The Comically Serious: He wants to be taken seriously by the scientific community, but it's not exactly easy with a name like "Pippy P. Poopypants". It really doesn't help that he doesn't realize it's an Unfortunate Name since everyone in his country has a silly name.
• Cool Shades: Angular ones that give him a perpetually angry or maniacal look, although they do occasionally change shape with his expressions.
• Cut Lex Luthor a Check: A humorous case where he actually did try to use his inventions to go legit, but the name kind of made that impossible.
• The Cynic: In the movie. He claims that a student's dream of world peace is "unattainable", and scoffs at Melvin's claim that "real power comes from within".
• Deadpan Snarker: The movie gives him a few snarky moments when he's not Chewing the Scenery like it's going out of style.
  "Oh, look at this. We've got a grade-A suck-up. Good to know, good to know."
• Einstein Hair: He has poofy hair that matches his Mad Scientist look.
• Even Evil Has Standards: His first-time clone is horrified when the original uses the Robo-Pants's nuke just to destroy George and Harold.
  • In the movie he leaves Ms. Anthrope (who is stuck on hold) alone, and refuses to get rid of the part of the brain that causes laughter simply because humans need it to survive.
• Evil Is Petty: He did shrink an entire school and hold all inside of it hostage just because people there found his name funny, after all.
• Freudian Excuse: People laughing at his name all the time led him to villainy.
• Genre Blindness: In the books, he took up a position as a teacher at an elementary school, believing that children were sweet and innocent and wouldn't laugh at his name. He was wrong. So very, very wrong.
• Giver of Lame Names: With his Name Change-O-Chart 2000, the professor forced everyone on Earth to change their normal names into silly names.
• Herr Doktor: The movie gives him a heavy German accent. "Swissland" is another name for Switzerland, which like Germany is in the Bavarian region of Europe, and speaks German.
• Hypocrite: He wants to rid the world of laughter, yet he frequently indulges in evil laughter, and even has a film of bloopers that he finds amusing.
• An Ice Person: He created a freeze ray in Book 8.
• Impossible Genius: Has mastered size-changing technology and time travel.
• Insufferable Genius: He's pretty egotistical about his inventions.
• Ironic Birthday: He hates being laughed at for his silly name, even going as far as wanting to wipe laughter off the face of the Earth in the movie. However, a Freeze-Frame Bonus in the movie shows on his file that his birth date is April 1st, 1953 or as it's more widely known as; April Fools' Day.
• Karmic Death: For attempting to blow up the planet, Tippy gets killed off permanently. Also, it's the mistreatment of his past counterparts that result in them sabotaging his machine resulting in their own deaths.
• Killed Off for Real: In Book 10, three separate times at that.
  • The first time, the original tries to active a nuke, causing his first time clone to punt him far, far away to cause the Extinction of the Dinosaurs.
  • The second time, the first time clone is sabotaged by the second, causing his freeze ray to go haywire and freeze him to death as the Ice Age happens.
  • The third and final time has the second time clone use an even bigger version of the nuke but is sent to the beginning of time thanks to a Heroic Sacrifice from Sulu and Crackers, and the ensured explosion causes the Big Bang.
• Large Ham: Voiced by Nick Kroll, and it shows.
• Mad Scientist:
  • In the books, he likes to invent, but he's not so mad until his Sanity Slippage.
  • Played straight in The Movie at his insistence:
    George: (reading his resume) It says here that you were a "genius inventor"?
    Poopypants: (slamming a mace down into the desk) Mad genius inventor!
• Make My Monster Grow: His Goosy-Grow 4000 can make things bigger, including his Mini-Mecha which he turns into a Humongous Mecha.
• Meaningful Rename: After attempting to give everyone in the world silly names, Professor Poopypants is advised by George and Harold to change his own name instead. Calling himself Tippy Tinkletrousers did not improve his situation.
• Nice Job Fixing It, Villain: When he goes back in time, he accidentally prevents Captain Underpants from ever existing, resulting in a Bad Future where all of the threats that Captain Underpants had stopped are now in play. He realizes his mistake and goes to fix it.
  • In the movie, He does this twice in a row. The first time was when he had the Turbo Toilet 2000 "eat" Captain Underpants. In doing so, he exposed CU to the pretty much radioactive leftovers from the school cafeteria, and it ultimately results in him getting real superpowers. The second time is when he's seemingly won after erasing George and Harold's sense of humor. He mentions the planet Uranus, which triggers the memory of how George and Harold first met, and gets them laughing again, which destroys the Anti-Humor machine and undoes its effects on the rest of the school.
• Not-So-Harmless Villain: Despite his ridiculous name and appearance and being a Butt-Monkey for most of the time, he is a highly intelligent, ruthless, violent and dangerous Mad Scientist whose inventions are powerful enough to put the world in peril.
• Oktoberfest: He speaks with a heavy German accent in the movie and comes from a country called "New Swissland."
• Omnicidal Maniac: Attempted to destroy the planet in book 10.
• Planet of Hats: He comes from a country where everyone has a silly name, and plans to export that tradition to the rest of the world by force.
• Recurring Boss: He's the one villain who keeps coming back over and over.
• Sanity Slippage: From well-meaning, brilliant scientist hoping to solve all the problems in the world or at least to teach young children the joy of science, to a crazy person hoping to give everyone in the world a name as silly as his, to a balls-out lunatic willing to do anything necessary to kill Harold and George, to an Omnicidal Maniac. Whoa! This is even more prominent in the movie, where he wants to eliminate all humor so no one will ever laugh at his name.
• Shrink Ray: His Shrinky-Pig 2000.
• Significant Birth Date: Of the ironic variety in the movie. Thanks to a Freeze-Frame Bonus, you see on his resumé that he was born on April Fools' Day, of all days!
• Shut Up, Kirk!: In the movie, when George and Harold try to talk him down.
  George: Your problem isn't that people laugh at you, but that you can't laugh at yourself.
  Poopypants: Oh, really, Oprah? Is that my problem?!
• Stating the Simple Solution: It takes two fourth graders to point out that it might have been easier to just change his name instead of holding the world hostage with shrink rays and Humongous Mecha. He claims he never even thought of that.
• Then Let Me Be Evil: George and Harold write a comic book about him trying to take over the world, and he finds a copy of it, suffers a psychotic break after reading it, and decides to actually take over the world. Nice job breaking it, George and Harold!
  • In the movie, he decides to play the villain role after seeing the boys' comic and finalizing his laughter removal machine. He even changes his outfit to match the one that George and Harold made for him in their comic.
  Poopypants: So George and Harold want a supervillain, huh? Well ask and ye shall RECEIVE!!
• Unfortunate Names: Just read it. The new name he gives himself (Tippy Tinkletrousers) is only slightly less embarrassing. When he came to America, everyone kept laughing at his name.
  • In the movie, it's changed to the more hilarious Pee Pee Diarrheastein Poopypants Esquire, which is even worse.
  • The professor later forces everyone on earth to change their names to unfortunate names with his Name Change-O-Chart. For example, Mr. Krupp is shocked when he became Lumpy Pottybiscuits.
• Villain Protagonist: Of Book 9.
• Unwitting Instigator of Doom: In the 9th book, A group of bullies that terrorized George and Harold's school when they were younger, and managed to terrified them with a curse involving "ghost pants" so much that they reformed, and the two kids became friends. However, Tippy, in his Robo-Pants, ends up traumatizing and snapping the bullies, and the following day ended with Mr. Krupp getting arrested due to being bruised when said bullies mistook him for a ghost. Because Krupp was fired, this caused the events of the first three books to play out, leaving to a Bad Future where the moon is destroyed, Talking Toilets corpses are strewn about the battered landscape, and gigantic super-zombies wandering the world.
• Where the Hell Is Springfield?: The few details we get about Poopypants's home country is that it is just southeast of Greenland,^note Which actually would describe Iceland that everyone there has a stupid name, and that people there have German-sounding accents.
• Would Hurt a Child: He was all too willing to hurt George & Harold in book 4, 9, and 10.
• Yodel Land: He is from New Swissland^note "Swissland" is another name for Switzerland and speaks with an exaggerated German-sounding accent in the movie.
• You Could Have Used Your Powers for Good!: He had every intention of using his shrinking and growing inventions for humanitarian causes like mass-scale waste removal and ending world hunger, but his attempts at promoting them in America went awry due to his unfortunate name.

Introduced in the Book Series

Dr. Diaper

A mad scientist who looks and dresses like a baby. He planned to destroy the moon, which in turn would destroy every major city, which would allow him to take over the Earth. In the UK version, he is called Dr. Nappy.

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• The Cameo: He makes an appearance in the same jail that Poopypants is sent to in Book 4.
  • In the movie, his name is mentioned when Captain Underpants is reading one of the comics the boys made.
• Cephalothorax: His head is his thorax.
• Colony Drop: His evil plan boils down to "destroy the Moon to rain chunks of it on the Earth, then rise and take over what's left of society after that".
• Cultural Translation: In the UK edition of the book, his name is changed to Dr. Nappy.
• Einstein Hair: Not as big and poofy as Professor Poopypants, but he's still got the typical Mad Scientist look.
• Generic Doomsday Villain: He doesn't have much character depth outside of wanting to destroy the world so he can take over it.
• Manchild: He goes around only wearing a diaper, and is the size of a toddler.
• Mecha-Mooks: He has two robot henchmen who help him carry out his schemes.
• Morally Ambiguous Doctorate: How he got the "Dr." part of the name is never specified, but he's still tried to blow up the Moon.
• Starter Villain: Series-wise, he's the first villain that George, Harold, and Captain Underpants ever face against.

Turbo Toilet 2000

A giant, vicious toilet who serves as the leader of the Talking Toilets and is the main villain of Books 2 and 11.

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• Adaptational Backstory Change: In the book series, he was a character created by the boys and was brought to life by the PATSY 2000. In the movie, he was an invention made by Melvin and was later remade into a formidable weapon by Professor Poopypants.
• The Brute: He's a hulking figure who often leaves a trail of destruction using his strength.
• Disney Villain Death: He meets this demise in Book 11 when Sulu and Crackers' interracial children drag the porcelain menace up into the sky and drop him.
• The Farmer and the Viper: A villainous example occurs in Book 11. When he corners Krupp, the principal begs for his safety by promising to lead Turbo to George and Harold so he can have his revenge on them. Once Krupp completes his part of the deal, the Turbo Toilet swallows him whole.
• Humongous Mecha: In the movie, Professor Poopypants enlarges the Turbo Toilet to enormous size and uses it as his main tool of destruction.
• Roaring Rampage of Revenge: In Book 11, the Turbo Toilet travels back to Earth seeking revenge against the heroes for killing his toilet army.
• Spikes of Villainy: He has spikes on his arms and boots.
• The Can Kicked Him: The Turbo Toilet gives Captain Underpants a brutal beating in both versions.

Talking Toilets

"YUM, YUM, EAT 'EM UP!"

An army of talking toilets who eat everything on sight.

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• Adaptational Backstory Change: Much like their leader, they were comic book characters who were created after the boys used the PATSY 2000 believing it to be a copy machine. In the movie, they come to life after being drenched by the toxic residue that was used to fuel the Turbo Toilet 2000.
• Broken Record: You'll know they're coming if you hear them chanting in the distance, "YUM, YUM, EAT 'EM UP! YUM, YUM, EAT 'EM UP!"
• Character Catchphrase: The only thing they ever say is "YUM, YUM, EAT 'EM UP!"
• More Teeth than the Osmond Family: They have vicious teeth that are perfect for eating.
• The Can Kicked Him: They have an interest in eating humans and are capable of swallowing them in a single flush.
• Getting Eaten Is Harmless: After being defeated, they regurgitate all of their victims, unconscious but unharmed and alive.
• Logical Weakness: Since the only thing they do is mindlessly devour everything in sight, they can be defeated by feeding them something poisonous, such as Foul Cafeteria Food.
• Too Spicy for Yog-Sothoth: In the books, they are defeated by George and Harold feeding them cafeteria food, making them violently ill.

Zorx, Klax, and Jennifer

A trio of aliens who disguised themselves as lunch ladies to brainwash the school so they can take over the world.

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• Aerith and Bob: Two of them are alien-sounding while the third is a common name among Earth women.
• Alien Invasion: Their grand scheme was to turn the students and faculty into zombie nerds and would then turn them into giant minions that would serve them as they conquer the Earth.
• An Alien Named "Bob": Jennifer.
• Beyond the Impossible: Zorx manages to snap his fingers... with a tentacle.
• The Cameo: The appear in The Movie during the end credits, suspiciously right after Edith's segment.
• Gender-Blender Name: Jennifer is a male alien with a female name.
• Killed Off for Real: They end up being killed after their UFO explodes thanks to the boys tampering with their fuel systems.
• Octopoid Aliens: They come off like this because of their green skin and tentacles for hands.
• Outside-Context Problem: They're the only alien enemies the main characters have faced, with all previous and future villains being human or created by humans.
• Scary Teeth: They have razor, sharp teeth to fit their evil appearances.
• Small Role, Big Impact: They only appear in Book 3 but are crucial as they unintentionally provide the boys with Super Power juice that would empower Captain Underpants and several others.
• A Villain Named "Z__rg": Zorx and Klax have this kind of stereotypical "evil alien" names.
• Villainous Crossdresser: They're all male-coded (although the book tries to obfuscate the issue by not referring to Jennifer using pronouns) but dress up as feminine cafeteria ladies (albeit rather poorly).

Evil George, Evil Harold, and Captain Blunderpants

"We are our own worst enemy."

The Purple Potty counterparts of our heroes. Rotten to the core, they enjoy using their supervillain creation to do whatever sinister schemes they want.

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• Arson, Murder, and Jaywalking: With Captain Blunderpants, Evil George and Harold have been able to get away with heinous crimes such as robbing banks, stealing electronics, and getting pizza with pineapple.
• Evil Counterpart: Evil George and Harold are mean-spirited and wicked children who make their own comic books. However, they are actually more talented than their good counterparts, creating much better-drawn comics with proper spelling and grammar. Inverted with Mr. Krupp, who is a nice principal with a good sense of humor.
• Evil Twin: That pretty much goes without saying.
• Felony Misdemeanor: Despite Captain Blunderpants committing all kinds of high-end robberies and larceny, what actually puts him on the police's radar is "grand theft pizza". Then again, this was the police of a Mirror Universe.
• Karma Houdini: Even after being defeated by the Arthritic Avengers and being sent back to their universe, it's more than likely that they'll go back to terrorizing their world with Captain Blunderpants, although now tiny-sized with seemingly no chance of reversing the process. They even manage to get their good counterparts arrested for the crimes they committed in the main universe, which later gets undone by Melvin after he tampers with the evidence.
• Too Dumb to Live: They attempt to blast George and Harold with the Shrinky-Pig 2000 after Captain Blunderpants is defeated, but they fall for the heroes tricking them into thinking they're holding it the wrong way, which causes them to flip it and shoot themselves.
• Weaksauce Weakness: Probably even more so than Captain Underpants. All you have to do is snap your fingers to turn Captain Blunderpants back into Nice Krupp.
• Would Hurt a Child: Captain Blunderpants was about to utterly pulverize George and Harold... but then Harold’s grandfather and George’s great-grandmother came to the rescue.

Kipper, Bugg, Loogie, and Finkstein

Kipper is the boy on the right with the key for a necklace and picking on Baby!Harold. Bugg is the boy beside Kipper with dark hair and a disgusting smile, Loogie has the tacky baseball cap and Finkstein has bangs covering his cruel eyes. Remember that now.

A group of bullies who used to torment Harold when he was in kindergarten. They've been able to get away with their despicable crimes since Kipper, the ringleader of the group is the spoiled nephew of Mr. Krupp.

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• Alliterative Name: Kipper Krupp.
• Blinding Bangs: Finkstein's hair almost always covers his eyes.
• Bring My Brown Pants: Finkstein wets his pants after finding dozens of spiders in his locker, courtesy of George and Harold.
• The Bullies: They get cheap thrills off of tormenting kindergartners.
• Butt Monkeys: Kipper & his stooges always fall victim to Kindergarten George & Harold's pranks.
• The Dividual: The four of them are always seen together and don't have many distinct personality traits aside from being sadistic jerks.
• Driven to Madness: When Tippy Tinkletrousers travels back in time to the exact moment and location of their Heel–Face Turn in the original timeline, they see his time-travel machine (which is shaped like a giant pair of pants). They immediately think they're seeing "The Haunted Pants of Wedgie Magee" in the flesh, go completely insane, and have to be carted off to a mental hospital.
• Dumb Jock: Kipper is a jock, but he's an idiot as well.
• Dumb Muscle: Clearly more brawn than brain—they beat up kids left and right, but get outwitted by a pair of prank-pulling kindergartners. George notes that Kipper's only weakness is that he's "kinda dumb".
• Generation Xerox: Kipper is taken after his uncle for being a cruel, sadistic, jerk who terrorizes children as a way of showcasing power over them.
• Goofy Print Underwear: After being driven insane by "the Haunted Pants of Wedgie Magee", Bugg reportedly "tore off his clothes and began dancing the hula while singing 'I'm a Little Teapot' as loudly as he could", with the illustration of the scene depicting him to wear white boxers with a heart print on them.
• Heel–Face Turn: After being scared straight by "The Haunted Pants of Wedgie Magee", they return all of the stolen money to the kindergartners they robbed and never bully anyone else for as long as they live.
• Humiliation Conga: They get put through a long extended one throughout Book 9 by George and Harold as retribution for bullying the kindergartners.
• Jerkass: They are assholes, especially to kindergartners.
• Jerk Jock: Kipper is on the school wrestling team and enjoys beating up kindergartners.
• Karma Houdini Warranty: Up until George moved to Piqua, Ohio, they would get away with tormenting kindergartners because Mr. Krupp was not at all suspicious of them. They did, however, fall victim to George & Harold's pranks.
• Scare 'Em Straight: George and Harold put them through a series of increasingly brutal pranks to make them think they've been cursed by a ghost called Wedgie Magee as punishment for their bullying.
• Screw the Rules, I Have Connections!: Kipper and his gang get away with bullying smaller kids out of their lunch money and giving them wedgies because his uncle is Mr. Krupp.
• Small Role, Big Impact: They only have a significant appearance in Book 9 but their presence is an important factor in George and Harold's lives; they not only become best friends because of the bullies but they also would develop their lifelong careers as comic book creators and professional pranksters.
• Starter Villain: Chronologically, they were the first "villains" defeated by George and Harold. They don't actually appear until Book 9.
• Teens Are Monsters: Preteens, actually. They're sixth graders who take pleasure in bullying younger kids.
• Unmanly Secret: Kipper doesn't actually have one, but George and Harold make it look like he does secretly putting dolls, dresses, and a friendship bracelet kit in his locker, getting his friends to laugh at him.
• Villainous Glutton: They intimidate a pizza delivery guy into giving them the pizza that "Wedgie Magee" bought for the kindergartners and gleefully eat it all in front of them. George and Harold get wise to this and trick them into eating pizza with double ghost chili peppers on each slice.
• Vitriolic Best Buds: Bugg, Loogie, and Finkstein find it hilarious when Kipper becomes the target of several pranks by "Wedgie Magee". They stop thinking it's funny when weird things start happening to them.
• Why Did It Have to Be Snakes?: Loogie is described to have "a severely intense fear of spiders", i.e. arachnophobia. Let's just say he did not take George and Harold's later revenge plans well.
• Would Hurt a Child: All four of them are notorious bullies whose favorite targets are kindergartners.

Introduced in the Animated Series

The Splotch

We are Splotch!

Voiced by: Clancy Brown

An evil, robe-like alien with plans for world domination. He was initially a sentient robe with a hostile attitude but it evolved after being dunked in the toxic residue.

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• Actor Allusion: Hates Captain Underpants so much that he declares that, "can be only one."
• Affably Evil: He admits that Splotch is a good villain name and genuinely apologizes to George and Harold on two separate occasions.
• Aliens Are Bastards: In his first appearance, he was very aggressive towards his host Jerry and attacked everything without bias. In his second appearance, he tries to take over the world.
• Character Catchphrase: "ROBES RULE!"
• Cool and Unusual Punishment: After he's apprehended by The Society of Robes, he's left imprisoned with the worst prisoner imaginable: a clown, who coincidentally was Captain Underpants's greatly appreciated cellmate during the time in which he was framed for crimes committed by Splotch.
• Evil Counterpart: After being drenched in toxic waste, the Splotch takes on an appearance that greatly resembles the Waistband Warrior himself. He uses this to his advantage in his second appearance.
• Evil Is Hammy: As expected from everyone whose voice is provided by Clancy Brown. Bonus points for being a pure evil example, given his incredibly deep voice.
• Evil Wears Black: His robe-like appearance is pitch black and he's a genuine villain.
• Expy: He's a deadringer for Venom.
• Fearful Symmetry: When the Splotch goes 'mano a mano' with CU, the two prove to be evenly matched in combat.
• Frame-Up: In his second appearance, he commits multiple crimes to convince the people that Captain Underpants did it so he can be arrested. With CU out of the way, the Splotch would be able to carry out his plans for world domination.
• Hidden Depths: He's implied to have an artistic talent when he recaps his first appearance and diabolical plans using well-drawn photographs.
• Logical Weakness: His army of robes ends up being defeated by two common things that affect clothing: static electricity and fabric softening wipes.
• Puppeteer Parasite: In both appearances, he needs to rely on a human host; the first was Jerry Citizen and the second was Mr. Ree.

Socktopus

Voiced by: John DiMaggio

A giant sock monster that captured the entire student body and faculty to harvest their stinky socks so he can take over Piqua.

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• Combat Tentacles: His main form of attack.
• Good Hurts Evil: He meets his defeat in the form of soap detergent which is made of 100% good.
• Gosh Dang It to Heck!: He has quite the colorful vocabulary. Though this was a given considering his voice actor.
• I Just Want to Be Loved: Before being defeated, Socktopus exclaims that he only wanted dirty socks such as himself to be appreciated more.
• Irony: He gets stronger using stinky socks and has a real hatred for shoes. Socks stink thanks to the countless hours they spend trapped inside shoes, soaking in their own sweat with no exposure to fresh air.
• Logical Weakness: What do you do to get rid of stinky socks? You wash them with soap detergent of course!
• Made of Evil: His genesis was a result of a bunch of socks being mixed with Mr. Krupp's toupee polish which is made of evil. Really!
• Verbal Tic: Almost every other word he says has the word “Stinkin’” in front of it.

Theodore Murdsly

Voiced by: Rob Riggle

A toilet paper salesman who tries to take over Jerome Horwitz. Having become a laughingstock among his peers for getting chocolate pudding on his pants resulting in the 'death sentence' title of Ted Turdsly, Murdsly is motivated to erase the name and create a new identity for himself as the greatest principal ever.

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• Badass Normal: One of the few, if not the only, members of CU's Rogues Gallery that is a normal human being. Villains such as Melvin or Poopypants don't count since they were already gifted geniuses before they turned to villainy, unlike Murdsly.
• Berserk Button: Ted Turdsely.
• Best Served Cold: Invoked. Murdsly spent roughly twenty years creating the memory wipes before he could take his revenge against Jerome Horwitz because they still use the Ted Turdsely nickname… and the wipes took way longer to develop than he thought.
  Harold: Makes sense.
  George: Can't rush science.
• Hair-Trigger Temper: It doesn't take much to set him off. Especially if it's the name that shall not be said.
• Ink-Suit Actor: Looks pretty much exactly like a slightly chubbier Rob Riggle.
• Kids Are Cruel: His childhood peers christened him with the nickname Ted Turdsely and never made him forget it. It's so bad that it's been an ongoing tradition among the students of Jerome Horwitz.
• Laser-Guided Amnesia: He created toilet wipes that are capable of erasing a person's memory along with making them extremely suggestible.
• Manchild: He often lets his emotions get the better of him, leading him to act very immature and unreasonable.
• Mini-Mecha: With Melvin's help, Murdsly gains a giant robot capable of erasing anyone's memory in an instance.
• Tragic Villain: At the end of the day, he is a miserable man who only wanted to start his life over after having it ruined since he was a child.
• Villain Has a Point: Oddly not from the villain but him trying to take over the school made George and Harold realize the whole "Ted Turdsley" tradition is a vicious circle that nothing good can come out of.
• We Will Meet Again: Before he escapes, he vows to return to enact his revenge against the boys and the whole school. However, he never came back.
• Woobie, Destroyer of Worlds: After a childhood of humiliation like his, it's hard not to pity him.

Smartsy Fartsy

Voiced by: Trevor Devall

A sentient and quite eloquent fart cloud that was brought to life by the Elevapor 2000, an invention of Melvin. After being offended by George and Harold's comic book featuring a dumb character of the same name (which was created before him), he attempts to get revenge on them to ensure that he gets respect.

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• Arc Villain: He serves as the main antagonist for the two-part season 1 finale.
• Balloon Belly: Not him himself, but it's what happens after inhaling him or any of his fart soldiers.
• Blow You Away: Being a sentient fart cloud, his attacks are all wind-based.
• Came Back Strong: A non-deadly example. After Captain Underpants inhales him, Smartsy is fused with CU's super-powered DNA which gives him a major power-up.
• Dude, Where's My Respect? / Mistreatment-Induced Betrayal: His start of darkness was after learning that his best friends initially wrote him as a stupid character for their comic along with being ridiculed by the school for his existence as a fart.
• Evil Former Friend: Before he turned evil, he considered George and Harold to be his best friends.
• Face–Heel Turn: He experiences one after finding out how George and Harold originally portrayed him as stupid.
• Green and Mean: From the climax of episode 12 to the end of the season 1 finale.
• Heel–Face Turn: He gives up villainy after he becomes a likable internet sensation thanks to his theatrical speeches.
• Nigh-Invulnerability: Smartsy and his army are immune to all physical attacks thanks to their airy forms.
• Sesquipedalian Loquaciousness: His choice in vocabulary is quite advanced because of his intelligence.
• Smart People Speak the Queen's English: He speaks with a British accent and is very intelligent.
• Straw Nihilist: Smartsy borders on this as he often laments how unfair he and his fellow farts have been treated as jokes by humanity and how they deserve better.
• Villain Over for Dinner: When Melvin's mother notices him, George, and Harold with her son, she assumes he has friends over and lets them stay for dinner, where she flirts with him.
• Villainous Crossdresser: He takes on the appearance of the tooth fairy to steal people's farts to create his army.

Melvinborg/Dr. Vil Endenemys (SPOILERS)

"He can't be bargained with. He can't be reasoned with. He doesn't feel pity, or remorse, or fear. And he will absolutely not stop, EVER, until his present self goes to Eliteanati Academy."

^{Click here to see him as "Dr. Vil Endenemys"}

Voiced by: Jorge Diaz

Melvin's cyborg self from the future. Under the guise of Dr. Vil Endenemys, he was able to have Krupp fired as well as getting George and Harold expelled at the end of the season finale. Along with taking over as the new principal, he also serves as the main antagonist for Season 2.

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• Adults Dressed as Children: He's a full-grown man yet he wears the same nerdy outfit his present self wears for school every day.
• An Arm and a Leg: The reason as to why Future!Melvin is a cyborg is because he was attacked by a swarm of Butt-erflies, sent to the future by George and Harold, which led to a near-fatal car crash that ruined the right side of his body.
• Arc Villain: For Season 2.
• Breath Weapon: He's capable of emitting fire from his mouth. Though he mainly does it when he's angry.
• Call-Back: Melvinborg being a cyborg who takes over the school is reminiscent of the plot point in Book 6 where Melvin tries to fuse himself with a robot to be more popular and powerful at Jerome Horwitz.
• Cheaters Never Prosper: Melvinborg purposefully rigs the education system to give his present self a huge advantage to make him more successful compared to everyone else. It never works out the way he wants to thanks to his Complexity Addiction and his inability to double-check his schemes.
• Complexity Addiction: He tends to create complex plans with unnecessary details to ensure his past self's entry into Eliteanati Academy.
• Crazy-Prepared: Knowing how dangerous and crazy things can get at Jerome Horwitz, Melvinborg installed a secret passageway in the principal's office that could take him to downtown Piqua or Mexico if necessary. Later he would create a panic room to keep him safe from the swarm of Butt-erflies.
• Cut Lex Luthor a Check: You'd think that with all of his groundbreaking inventions that Melvinborg would have made a decent future for himself and would have no need to push his younger self to get into Eliteanati Academy. Apparently, this never passed through his brilliant mind.
• Cyborg: His right half is all robotic and allows him a variety of weapons and gadgets to use when needed.
• Distressed Dude: Despite being the main villain, Melvinborg often becomes a victim to several of the monsters of the week.
• Dramatic Irony: For all of his efforts in trying to get his present self into Eliteanati Academy while sabotaging everyone else's education, it actually results in George and Harold, the two people he hates with all of his heart, getting accepted into his dream school instead.
• Evil Genius: He's Melvin's future self.
• Evil Is Hammy: Even more so than the present self.
• Evil Is Petty: Melvin has always had a petty side, but his future self actually takes time between his schemes just to commit small acts of extreme pettiness, especially on Krupp who he apparently hired for no other reason than to make a fool out of him.
• Failed a Spot Check: One of his defining flaws is how he doesn't double-check his plans to see if anything can mess them up. It's this carelessness that often results in all of his plans backfiring.
• The Farmer and the Viper: Even after George and Harold manage to destroy the nanobots and save everyone, Melvinborg insisted his present self to leave Captain Underpants' brain without them.
• Fate Worse than Death: After realizing what a monster his future self is, Melvin decides to never become him; thus erasing Melvinborg from existence.
• Forgot About His Powers: Melvinborg's robot side comes equipped with helpful powers (a retractable arm, a laser eye, etc.) The only problem is that he forgets to activate them in moments that would make them useful.
• Future Me Scares Me: It's actually more along the lines of Future Me Infuriates Me. As Season 2 progresses, Melvin begins to lose patience with his future self because of his complicated plans that always backfire and how he always underestimates George and Harold despite their success rate. Played straight, however, when he reveals his intentions to leave George and Harold for dead in Krupp's brain. This is the final straw for Melvin, who's had enough of himself and wipes him out of existence.
• Hidden Depths: Turns out he has an interest in country music.
• Horrible Judge of Character: No matter how many times George and Harold successfully foil his convoluted schemes with their abilities and dumb luck, Melvinborg doesn't think much of it and brushes them off as hopeless dopes. This is something that his present self is aware of and constantly chastises him for it.
• It's All About Me: Taken to the extreme. He transforms Jerome Horwitz into a devil's paradise for his younger self; from changing the curriculum to meet his advanced standards to plastering his image everywhere for all to love and worship him.
• Jerkass: He hasn't changed one bit since he was a kid. The Season 2 finale suggests that he became even worse.
• Jerk with a Heart of Jerk: He does aid George and Harold in saving Captain Underpants from the nanobots taking over his brain in the season 2 finale, but if you really think it was a sign he could have a nice side, think again. Near the end, he even tries to abandon the two in Krupp’s brain to die, only being stopped by his present self.
• Never My Fault: Even after his plans end up blowing up in his face, he outright refuses to accept the responsibility on his end.
• Reversible Roboticizing: An unusual case of this trope, where the cyborg part becomes optional for Time Travel reasons due to the present-day Melvin Sneedly renouncing the Evil Plan to kill Captain Underpants that Melvinborg wanted carrying out, causing Melvinborg to be Ret-Gone.
• Shadow Archetype: In a nutshell, Melvinborg is what Melvin will end up becoming if he allows his inflated ego, arrogance, selfishness, his belittling of others, to continue unchecked into adulthood.
• Tempting Fate: Does this quite a few times throughout Season 2 regarding his inventions. It goes exactly how you think it does.
• Took a Level in Jerkass: Melvinborg is shown to be a bigger jerk than his child self. And that's saying something.
• Trademark Favorite Food: He has a thing for milkshakes; he even has a milkshake dispenser in his office.
• Transforming Vehicle: In the Season 2 finale, his robotic half can transform into a hovercraft that can carry multiple people.
• Walking Spoiler: It's pretty hard to talk about Season 2 without the big twist in the Season 1 finale involving him and his takeover of Jerome Horwitz.
• What Were You Thinking?: He gets called out by George, Harold, and his present self when the Doom Dome in the season finale goes haywire and begins to attack them with dangerous machines, all of which Melvinborg created as part of the Tattle Trials.

Teachertrons

Bionic teacher drones created by Melvinborg to replace the Jerome Horwitz faculty as a way of providing his younger self an education that suits him.

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• The Bus Came Back: They return in the Epic Choice-O-Rama special as the patrol officers of the underground Teacherville.
• Fun-Hating Villain: They are programmed to eliminate any signs of fun having or tomfoolery, which makes it harder for the boys to get away with making comics or pulling pranks.
• Hoist by Their Own Petard: The advanced lessons in robotic engineering the robots provided would be their own undoing as George and Harold would use that knowledge to defeat them in the climactic battle.
• Kill and Replace: Thankfully, they're not murderous fiends, but the Teachertrons do round up the human faculty members and trap them in the teacher's lounge while they took over their classrooms... which makes this the child-friendly version of this trope.

Croco-bats

An army of genetically engineered animals created by Melvin's You-Choose-You-Fuse 2000 to destroy recess.

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• Attack Animal: Melvin created them in the hopes of ruining recess for everyone with their viciousness.
• Bat Out of Hell: They are part bat, after all.
• Disc-One Final Boss: They're easily taken care of when George and Harold learn about their favorite food and instantly make way for the real monster of the episode...
• Early-Bird Cameo: They actually appeared in Episode 2 of Season 2 where they find Other Sophie in the jungles of Ecuador and make her their queen.
• Mix And Match Creature: As their name suggests, they're made of crocodiles and bats.
• Never Smile at a Crocodile: They're aggressive like the crocodile.
• Really 700 Years Old: George and Harold manage to transport them back into the prehistoric era where they're able to survive past the Ice Age and thrive well into the present time.
• Trademark Favorite Food: Their favorite meal is Melvin's mother's meatloaf.

Butt-erflies

A swarm of genetically engineered insects created by George and Harold in an attempt to annoy Melvin. They actually turn out to be more dangerous than what their cute appearances suggest.

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• Evil Smells Bad: Since they're part butts, they're able to weaponize their farts to smoke out the students who were hiding in the cafeteria.
• Killer Rabbit: They're pretty adorable when they're not trying to rip up your flesh.
• Mix And Match Creature: Of a butterfly and a human butt.
• More Teeth than the Osmond Family: The better to eat you with.
• Punny Name: They're butterflies that look like butts. You do the math.
• Small Role, Big Impact: Despite being the Monster of the Week, the ending reveals that they were responsible for Future!Melvin becoming a cyborg. Granted it was George and Harold who sent them in the future in the first place, it still stands that they led to his near-fatal car crash.
• The Swarm: They are part bugs so they would travel and attack like this.
• Trademark Favorite Food: They love eating the drywall from the school.

Dr. Disgruntled

A fictional evil scientist that frequently appears in George and Harold's comic books.

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• Arch-Enemy: To Captain Underpants. His two main appearances involve him trying to create death traps to defeat the waistband warrior.
• Bald of Evil: He has no hair and he's a supervillain.
• Cool and Unusual Punishment: After failing to defeat Captain Underpants in his second appearance, he ends up having to work as a sidekick on a radio talk show and it's clear that he does not enjoy it.
• Evil Genius: His main archetype.
• Trap Master: He loves making traps. Especially if they're designed to kill CU.

Laserlightmare

A monster made out of Hard Light created by Melvin as a living prison for his fellow campers, a job very clearly doesn't like.

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• Being Evil Sucks: As he notes, he doesn't want to contain, but rather entertain.
  Melvin: You had ONE job!
  Laserlightmare: But it's not the job I want!
• Brainwashed and Crazy: Done twice, first when Melvin activate the Lazerker Protocol, and again when Mr. Krupp presses Melvin's Revention 2000, the latter of which causes him to destroy the entire camp.
• Energy Weapon: On top of being made of Hard Light, he can also fire laser beams from his hands.
• Hard Light: He's made of pure light, and can shred things into just by walking through them.
• Puzzle Boss: Due to him being made of Hard Light, attacking him directly is next to impossible. Captain Underpants defeats him by smacking him with mirrors, knocking him back into a lake and distorting him.
• Red Is Violent: Once Melvin activates his Laserker Protocol, he shifts from green to red, and becomes far more villainous.

The Biglyans

(Garg) voiced by: Peter Hastings
(Sqworg) voiced by: David Koechner

A race of intergalactic conquerors known for their humongous stature and peanut-sized brains. They are the main antagonists of The Epic Tales of Captain Underpants 'IN SPACE.

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• Big Bad: They're the main villains of the fourth season.
• Dumb Muscle: While they're presented as being hulking idiots, they were stated to be quite intelligent before being rendered stupid by the Litlytes as part of their escape plan.
• Genius Ditz: Despite their reputation of being idiots, they're actually shown to be quite clever when outsmarting the humans.
• The Starscream: Near the end of the season, they decide to make Melvin their king and provide him an armada to bring to Earth so that the nerd can become famous. It's actually an elaborate ploy to lead him to his home planet to conquer it.