!!The PowerTrio
!!!Ickis
Our main hero, [[MrViceGuy flawed as]] [[AntiHero he is]]. Son of the legendary Slickis, he has a lot to live up to... but his {{Ugly Cute}}ness, nervous disposition and self-confidence issues combined with his tendency to slack off keep working against him. Still, one shouldn't underestimate him based his looks or personal problems; his [[SizeShifter scaring]] [[OneWingedAngel skills]] are nothing to laugh at...

* ArtEvolution: In "The Switching Hour: Part 1", he has noticeable temple arms next to his eyes suggesting that he wears glasses. Later episodes, he doesn't have them.
** He's actually wearing glasses while disguised as a human kid in "The Switching Hour: Part 2" (clearly visible underneath the backwards ball cap he dons even though the kid he's imitating didn't wear glasses, which suggest Ickis already had a pair with him), and Ickis wears glasses in most scenes from "Monsters Get Real" which was intended to be the series pilot. Either he switched to contacts later, or the animators got tired of drawing them.
* AcquiredSituationalNarcissism: Give him a situation where he [[StatusQuoIsGod temporarily]] gets popularity, riches or notoriety... and about five seconds. Hello again, [[{{Pride}} cocky]]-[[{{Jerkass}} ass]] Ickis!
* AesopAmnesia: A cronic case. See above.
** To be fair, he always becomes cocky for a different reason (he completes a successful scare and gets praised by the Gromble and Dizzle, he's farther along on his homework than Oblina for a change, he finds a bunch of toenails and is temporarily wealthy, he's new in school and thinks having a famous father automatically means he will be respected and revered simply for existing.) The Aesop is never presented as "don't be cocky" but "don't be cocky if *insert situation* happens" so it's likely Ickis never makes the connection that cockiness all by itself is annoying or wrong.
* BerserkButton: Being mistaken for a bunny. He's not cute!
* BigDamnHeroes: Surprisingly good at these when he put his mind to it.
* ABoyAndHisX: Once adopted a puppy that he named Fungus and tried to hide from the Gromble.
* BrilliantButLazy: Despite his self-doubt, he actually had real ''talent'' and wit; however, he spent a lot of time [[TheSlacker slacking off]] and neglecting his scares, leaving them to the last minute... and then panicking about it.
* CatchPhrase: "I hate my life." Doubles as a Shout Out to Rocko's Modern Life, where Ed Bighead (also voiced by Charlie Adler) expresses the same refrain. He has a few other repeated sayings like [[Music/JamesBrown "On the good foot!"]], "I'm bad!" and "No way!" that are used sporadically, but not quite to the same extent as "I hate my life."
* TheChosenOne: There are definite elements of this. In the first season, "Where Have All The Monsters Gone", The Great Pool, the collective embodiment of all monsters, declares Ickis is the one who will lead the other students to rectify the lack of fear crises -- which he does. In the second season, Ickis is the monster selected to undertake the once every 400 years quest to find the Holey Pail; this is a big deal in monster society, and the last monster to quest for it was none other than the Gromble.
* ClarkKenting: His Super Monster costume is nothing more than a towel for a cape, and underpants for a mask. It does at least cover his ears, which seem to be viewed as his most distinguishing feature.
* CrouchingMoronHiddenBadass: Most commonly kind of goofy, but when he gets serious...
* CuteButCacophonic: Ickis is the least scary-looking of the regular monsters, but he has a very high-pitched voice. This isn't entirely a bad thing in monster culture; when he and Krumm are mashed together to become Krickis, Krumm is genuinely pleased he can now whine like Ickis does.
* FantasticRacism: When Ickis becomes spontaneously combustible, almost all the other monsters react with fear and refuse to be around him. Horvak takes it the farthest, by actually pulling Krumm out of the Academy temporarily.
* ForbiddenFruit: Was absolutely fascinated by human culture, despite the Gromble forbidding everything to do with it.
* GuileHero: Since he didn't have much in the way of sheer physical strength, and going OneWingedAngel couldn't solve all his problems, he tended to rely more on quick thinking and {{Indy Ploy}}s.
* HiddenDepths: Ickis is a surprisingly good dancer, as shown in multiple episodes.
** FridgeLogic: And since dancing seems to be part of monsterkind's [[BizarreAlienReproduction reproduction process]], [[GettingCrapPastTheRadar that means...]]
* InferioritySuperiorityComplex: {{Inverted}}; he has one, but instead of the high-and-mighty airs being his default mode, he only assumes them when given the opportunity. The rest of the time, the emotional mess underneath is fully exposed.
* InterspeciesFriendship: While monsters in general seem to look down on humans, Ickis really seems to be quite amiable towards them; whilst he still scares them because he has to, and enjoys doing so, he really does sit in PunchClockVillain territory with the fact he's quite companionable towards them if given the opportunity. He makes fairly good friends with Bradley, despite their less-than-stellar first meeting, and in one episode becomes attached to a blind old blues player to the point of going on one of his most impressive physical transformations to help him.
* JockDadNerdSon His father has won a few trophies, and ribbons, and plaques, and more trophies... A recurring theme is Ickis despairing of ever matching the Great Slickis' exploits. It's telling that when the Gromble forces him to become a LastMinuteEntry in a wave-riding competition, the same competition that his father NEVER lost, everyone is betting on Ickis... to lose. In a surprising twist, Ickis proves that he could have won that event, but gives up a sure victory to go back and save Krumm.
** Unusually for this trope, however, his father isn't really that demanding and is quite understanding that his reputation is a lot to live up to. In his introductory episode, he deliberately showcases one of his own embarrassing failures to help his son realise that even The Great Slickis didn't start out so great, and he's highly proud of Ickis's above mentioned moral victory.
* {{Keet}}
* KillerRabbit: Ickis's transformations include fangs and claws that certainly look quite nasty, even before he starts growing larger. Even when he doesn't have them, he's got a nasty bite, and he's actually pretty good at making scary sound effects (screeching, scraping claws, gnashing fangs). It's usually when he appears and people see how much like a rabbit he looks that they tend to stop being scared.
* LargeHam
* LetsGetDangerous: When the chips are down is when Ickis tends to forget about his issues and just go with his instincts.
* TheMcCoy
* MoodSwinger: Depending on the moment, he could go from [[{{Pride}} cocky]] {{Jerkass}} to [[WideEyedIdealist wide-eyed]] [[NaiveEverygirl naivete]] to DeadpanSnarker to panicky [[TheWoobie Woobie]].
* MrViceGuy
* [[NaiveEverygirl Naive Everymonster]]
* NotSoDifferent: From his father or the Gromble.
* OtherMeAnnoysMe Is conned into creating 5 clones in one episode. The clones fulfill his 5 scares in a day assignment, enabling him to play Sewerball. In a rare moment of glory Ickis wins the game. Too bad for him the clones escape from his dorm and annoy The Gromble, The Snorch, Zimbo, Krumm and Oblina, leaving Ickis highly upset.
* ParentalIssues
* PingPongNaivete
* RedEyesTakeWarning: A signal he was going to start looming was his eyes turning red. The accompanying noises made it sound like they were actually ''filling with boiling blood''.
* ShipTease: The clone Ickis seems to regret the most is Chickis, the lecherous clone who tries to kiss Oblina, which he claims he will never be able to live down. Bear in mind that Ickis got awfully jealous when Oblina was squishing on the popular Gludge, once confessed that he didn't know what he would do without her, and his version of how they scared an operahouse full of humans had Ickis rescuing the nervous, starry-eyed Oblina who all but swoons over his bravery.
* SizeShifter: Called 'looming' or 'growing', which also functioned as a OneWingedAngel mode for his victims. Of all the monsters, he seems to be the most adept at it, once growing bigger than an apartment building.
* StrongFamilyResemblance: He's basically a somewhat scrawnier version of his dad.

!!!Krumm
Ickis's best friend and fellow underachiever, a squat, hairy pink monster with [[EyesDoNotBelongThere free-rolling eyes]] that he normally carried around in his hands. Cheerful and carefree, he never stressed about scaring as much as his roommates, just enjoying whatever misadventures they got into.

* BrilliantButLazy: Krumm is actually more intelligent than he lets on (much to the surprise of The Gromble), to the point where he's actually scored second behind Oblina in scaring at least once. He only acts dumb because there's less pressure on himself.
* {{Cephalothorax}}
* {{Curse}}: Suffered from the Curse of the Krumm for a period of time, but managed to break it with the help of his friends.
* EyesAreUnbreakable
* EyesDoNotBelongThere
* TheFool
* HisNameReallyIsBarkeep: His family is called "the Krumm". Apparently, Horvak wasn't very imaginative when it came time to name his son.
* TheKirk
* StrongFamilyResemblance

!!!Oblina
Though her family had enough toenails that she could lounge in the lap of luxury for the rest of her life, Oblina chose to attend the Monster Academy. Since she could [[OneWingedAngel pull her insides out,]] she quickly became top scarer in their class, despite having two of the ''worst'' students as her roommates. Frequently tries to get them to take their studies more seriously, and isn't above gloating whenever ignoring her advice gets them in trouble... but isn't above the antics herself, and [[OddFriendship still considers them her best friends]].

* ActionGirl: Or the scarer equivalent.
* BalloonBelly: She is built around this trope. It's usually the horrible way her stomach growled in [[SickEpisode internal affairs]] and what happens if she eats something bigger than her head.
* BecomingTheMask: Happened once; while disguised as a human to gather information on them, she had a bad reaction to cotton candy and ended up believing she was really human.
* BracesOfOrthodonticOverkill: After a youthful indiscretion of brushing her teeth ''once'', she had to get a set of these to ''un''straighten them. This grabbed the attention of the RomanticFalseLead -- or rather, his reflection off of them did...
* GrowlingGut: This happens to her when she gets infected by parasites.
* IWarnedYou: A common refrain on her part.
* InsufferableGenius
* LonelyRichKid
* OneWingedAngel: You know the one...
* ParentalIssues
* TheSpock
* TeachersPet
* ToiletHumor: She burps when she eats a shoelace, which, sounds quite weird.
* WhatTheHellIsThatAccent: Speaks with a vaguely British accent, even though she is an American monster. Notably, her parents have a different accent.

!!Staff Members
!!!The Gromble
Headmaster and head teacher, The Gromble certainly isn't afraid to berate, belittle and punish his students whenever they falter in their scaring or studies. Particularly likes to single out Ickis and his friends -- though admittedly, they ''do'' bring a lot of it down on themselves. For all his harshness, he really does care about his students and wants to see them succeed -- even if he has to beat every scrap of hard work out of them!

* AgonyOfTheFeet: Those fetching red high-heels were accidentally obtained during his first trip into the human world... when they got wedged on his feet.
* BadassTeacher
* CampStraight: He was melodramatic and wore red pumps, but in one episode had a crush on the female librarian.
* DeanBitterman
* {{Expy}}: The Gromble was patterned in voice and design after the [[WesternAnimation/YellowSubmarine head Blue Meanie]].
* JerkWithAHeartOfGold: See PetTheDog
* LargeHam
* NiceShoes
* NotSoDifferent: It was implied several times that when he was Ickis' age, he suffered a lot of the same problems and stumbling blocks.
* PapaWolf: He'll go to great lengths for his students, and doesn't care if you're a member of his academy or not if he catches you toying with his students he '''''will''''' make you regret it.
* PetTheDog: Getting these moments now and then showed [[HiddenHeartOfGold how much he really cared about his students]].
* RedEyesTakeWarning: A key indicator that you '''''really''''' ticked him off is that his eyes turn red (much in the same manner as Ickis' when he starts to loom, complete with the blood filling sound)
* SadistTeacher[=/=]SternTeacher
* SpellMyNameWithAThe
* StrongFamilyResemblance: To his mother.
* VagueAge: Possibly a RetCon? In one episode he was depicted as a young teacher just starting his career in the late 1700s, and another has him as a child in the 1920s.
** Teaching in the 1700's is more probable. He embarked on the Quest For The Holy Pail when he was a student... 400 years ago. The Gromble would have to be really 500 years old for some of his comments to even make sense, although it still seems like an exaggeration to say he hasn't seen another monster in centuries.
* VerbalTic: Switches between a sweet (and extremely sarcastic) tone of voice, a sinister growl, and over-the-top screaming at the drop of a hat.
-->'''The Gromble:''' Oh, Master Ickis, how ''inquisitive'' you are today! It is so '''''ANNOYING!!!'''''
* VillainousCrossdresser

!!!The Snorch
TheUnintelligible monster who handles all the {{Cool And Unusual Punishment}}s rule-breaking students have to suffer. Very intelligent, with a love for the very same things he uses as punishments, like opera and square dancing. Unfortunately, the communication barrier makes it difficult to share his interests and thoughts with others...

* BerserkButton: Don't mess with his golden hair... he's very protective of it.
* CoolAndUnusualPunishment: His speciality.
* HiddenDepths: The Snorch honestly enjoyed classical pursuits like opera and was highly intelligent.
* LoudOfWar: Music is a preferred punishment method of his.
* SpellMyNameWithAThe
* TheUnintelligible

!!!Zimbo
As the only monster capable of understanding The Snorch -- and a craven little coward with a tiny body and no real physical strength of his own -- Zimbo likes to stick close to The Snorch and leech off his fearsome reputation. Also uses his size to his advantage by spying on the students and reporting back to The Gromble.

* TheInformant
* {{Jerkass}}
* TheStoolPigeon
* TranslatorBuddy He is the only student who understands The Snorch's mutterings... although on the rare occasion where he disagrees with the Snorch, Zimbo will deliberately offer an incorrect translation.

!!Parental Units
!!!Slickis
Ickis's father and the most famous graduate of Monster Academy. Living up to his legacy is quite the responsibility...

* TheAce
* {{Acrofatic}}: Flashbacks show him as a chubby bonsty, and even nowadays he's quite a bit broader and heavier than Ickis. Yet Slickis still has an easy time scaring humans, can stand up to a tank, and is great at monster sports (evidenced when he bowls a perfect game of Gorblats.) He might be a BigEater as he cheerfully suggests buying a large amount of Slime Pies, and his first choice when listing father/son activities was to go forage for food.
* BoisterousBruiser: Extremely friendly, cheerful and happy, making yet another stark contrast with his emotional son.
* GenerationXerox
* MinorMajorCharacter: He's one of the most famous monsters to have ever graduated from the Gromble's Academy and father to Ickis, yet he only appears in 5 episodes (one of which is a flashback, and another is part of a dream sequence.)
* NotSoDifferent: Has admitted that he didn't have the easiest time in school and was a lot like Ickis.
* PapaWolf: Risked his own life to save his son's from being flattened by a tank in a botched scaring attempt certainly counts
* ParentalIssues
* ScarsAreForever: As an adult his ears are torn in several places.
* StrongFamilyResemblance: Was a little taller than Ickis and had a stockier, sturdier build.

!!!Horvak
Krumm's father, an equally cheerful monster who makes his living as a muck farmer. Has only one eye, and wears a black glove over his empty hand.

* {{Curse}}: Like his son, suffered the effects of the Curse of the Krumm. ''Unlike'' his son, was never able to break it, and [[spoiler: lost his stench for good]].
* EyepatchOfPower
* EyeScream: He attempted to scare people in pre-Revolutionary America, but dropped one of his eyes as a soldier dropped a box of musket balls. The soldier grabbed Horvak's eye by mistake, loaded it and... well, it was the Shot Heard Round the World.
* FantasticRacism: He doesn't want Krumm to attend class with a combustible monster, and tries to come up with an excuse for Krumm to leave.
* GenerationXerox
* PermaStubble
* StrongFamilyResemblance: Basically looked like an older version of his son (minus one eye).

!!!Sublima
Oblina's rich and overbearing mother. She disapproves of her daughter becoming a common scarer, and would much rather see her return to the lap of luxury.

* MyBelovedSmother

!!!Skeech
Oblina's meek and submissive father, who only wants to see his wife and daughter happy.

* HenpeckedHusband
* OpenMindedParent: He is in favor of his daughter scaring career and stands up to his wife to aloud Oblina to return to the Academy.

!!Important Humans
!!!Simon D. Hunter
As his title implies, Simon is a self-declared monster hunter, determined to break the masquerade and prove once and for all that he isn't insane. Develops a very personal grudge against Ickis after the little monster thwarts his plans and keeps humiliating him. His surname and middle initial were given in his expired driver's license in the episode "Battle of the Century."

* EvenEvilHasStandards: Despite constantly trying to capture the monsters, Simon means no particular harm to them. In the episode "Showdown" he even rescues Ickis from some more ruthless monster hunters who want to kill Ickis instead of capturing him alive.
* TheHunter
* MeaningfulName: Simon D. Hunter...Simon the hunter.
* ItsPersonal
* LargeHam
* NotSoHarmlessVillain
* SmallNameBigEgo
* TheyCalledMeMad

!!!Bradley
A somewhat nerdy young boy who became curious about monsters after first encountering them. Briefly became Simon's apprentice; however, when Ickis told him [[TheyWouldCutYouUp what would happen if]] [[BrokenMasquerade monsterkind was revealed to humanity]], he promptly [[HeelFaceTurn helped them escape]] and became a SecretKeeper.

* ChekhovsGunman
* HeelFaceTurn
* SecretKeeper