[[WMG: Cooper "Coop" Burtonburger]]
->Voiced by: Erin Mathews

A 10-year-old boy who knows Kat is evil. He tries to stay out of trouble, but is often humiliated and injured when trying to prove Kat's true identity. He gets the blame for everything Kat ruins in the house. Coop sometimes thinks Mr. Kat plans is to take over the world, but Mr. Kat's plans are to return home or just to get food for himself. Coop may have misunderstand Mr. Kat most of the time. Coop's father thinks that Cooper is insane for thinking that Kat is an evil alien. Only Dennis, Coop's best friend, and later Fiona, as well, believe in him. The Burtonburger's neighbor, Old Lady Munson, hates Coop, but favors Millie, and she has a many greats-grandniece, Fiona, who Coop likes. Coop has brown hair and blue eyes.

* TheAce - Subverted. Coop ''could'' have easily been the smartest, most popular kid in town if he didn't have Kat to worry about.
* ButtMonkey: Thanks to Kat ruining his life.
* TheCassandra: Nobody (except Dennis and Fiona) ever believes him about Mr. Kat, even when trying to use photos
* EnemyMine: Whenever a larger threat appears, such as Mr. Cheeks, Kat and Coop will work together.
* {{Expy}}: Lets see a kid who finds out that a certain newcomer is an alien, becomes [[ArchEnemy Archenemies]] with them, tries to warn people about it, but don't believe him probably because of ignorance and obliviousness. Plus he really isn't popular in school, so uh... if he ever puts on glasses and some geeky attributes he could pass off as [[InvaderZim Dib.]]
* FriendlyEnemy: To Kat. They are capable of getting along and working together for a common goal quite well. They even had a form of truce in the first Christmas special. However, these are rare occasions and they often go right back at each other's throats.
* GenerationXerox - Coop's life is awfully similar to his dad's childhood.
* GoodIsNotNice: Although he's the main protagonist of the show, Coop is sometimes a ''big'' giant asshole like much of the cast, especially to Mr. Kat and his sister.
* HeterosexualLifePartners: With Dennis.
* TheHero: He's of the LoserProtagonist variant, but is nonetheless still the hero.
* MissingMom: His mother is not mentioned at all and no clue is mentioned on her. He may have gotten her blue eyes from her given that besides them, he otherwise heavily resembles his dad.
* OnlySaneMan - He along his friend Dennis and later Fiona seem to be among the few well-adjusted folk in town.
* PintSizedPowerhouse: He is very skilled at fighting for a ten year old.
* TheScapegoat - If something goes wrong, no matter what the circumstances, people blame Coop.
* WillTheyOrWontThey - With Fiona
** TheyDo - They got married after the show.

[[WMG: Mr. Kat]]
->Voiced by: Kathleen Barr

A space alien who looks like a hairless Sphynx cat. Kat is adopted as a stray kitten by Millie Burtonburger. Blaming Coop for being stranded on Earth, Kat hates Coop though at times he and Coop get along, in-fact whenever trouble threatens both of them they work together as revealed in "Just Me and Glue." Kat tries to get home only to be interfered with Coop. There is a possibility that he likes Millie as he has been acting affectionate with her and even sleeps in bed with her. However, his affection for Millie may be fake. For example, in the episode "One Big, Happy Family" when Millie fell for a trap Mr. Kat made, Mr. Kat tried to save her. It's unknown whether if it was because he cared about her safety or she would just mess up his plan. In "Pet Peeved" Mr. Kat got jealous when Millie ignored him, this shows that Mr. Kat truly loves Millie with all of his heart.

* AlienAnimals - Kat and the rest of his race happen to look and act like Earth cats, providing the plot of the show.
%%* AxeCrazy - When provoked.
* BalloonBelly
** Kat gets one in "Fishy Frisky Business" after he gobbles up Colossal Coupon Mart's whole supply of Fishy Frisky Bits and ballooning bigger than the store.
* BigBadWannabe: He's the antagonist of the show, but becoming the ButtMonkey prevents him from getting close to the BigBad status.
* BrilliantButLazy: A very intelligent being, but prefers to lounge around and do things for himself. Turns out this is a trait for his entire species; heavily smart, but too lazy to clean up after themselves, hence why they go from planet to planet.
* ButtMonkey: He often gets his karma thanks to Coop.
* CatsAreMean: He's a cat-like alien and the antagonist of the show so no surprise
* {{Deuteragonist}}: The antagonistic kind.
* DevilInPlainSight - It's surprising how few people notice what he really is.
* TheDogIsAnAlien: As Coop constantly tries to inform everyone.
* EnemyMine - Whenever a larger threat appears, such as Mr. Cheeks, Kat and Coop will work together.
%%* FormallyNamedPet
* FriendlyEnemy - To Cooper. They are capable of getting along and working together for a common goal quite well. They even had a form of truce in the first Christmas special. However, these are rare occasions and they often go right back at each other's throats.
* GadgeteerGenius: He can construct lethal weapons from household objects.
* HairTriggerTemper: At times, it seems like it takes little to set Kat off.
* PintSizedPowerhouse: Although he's the size of a cat, his physiology and skill make him very dangerous.
* RoboticReveal - "Nip/Duck" reveals that Kat is actually a cyborg.
* VillainousGlutton - He really loves cat food.
* WoobieDestroyerOfWorlds: He is more than capable of destroying or enslaving the world, and has attempted to a few times. However many episodes indicate he really misses his family, and his "schemes" are just attempts to go home.

[[WMG: Millie Burtonburger]]
->Voiced by: Kathleen Barr

Coop's 8-year-old younger sister and the "owner" of Kat. She loves Kat and is oblivious to the fact that he is an alien, and sometimes, she interrupts his evil plans. She can scream so loudly that the whole town can hear her. They call her the "master manipulator". Her father does everything she says. Millie has black hair, and she wears red glasses.

* AnnoyingYoungerSibling: She generally annoys Coop for a variety of reasons.
* BitchInSheepsClothing: She acts all sweet and innocent but is a [[ManipulativeBitch master manipulator]], especially to Coop.
* BlindWithoutEm: Oh yes. She does not have good sight without her glasses
* DaddysGirl: Mr. Burtonberger will often listen to Millie more than Coop.
* HiddenDepths: Surprisingly loves monster trucks as much as her brother does.
* IdiotSavant - Millie will usually turn out to be pretty skilled at whatever activity Burt tries to get her interested in - Whether it's building houses of cards or running the family store. But not at bowling, it turns out.
%%* {{Jerkass}}
* MakeMeWannaShout: She can scream really, really loud.
* ManipulativeBitch: Her profile states she is a master manipulator, and is always able to get her way, often using her deafening scream. Even [[HatesEveryoneEqually Old Lady Munson]] gets along with her.
* MissingMom: Much like Coop, she doesn't speak of her mom. Though presumably, she got her looks from her.
* MoralityPet - To Mr. Kat. The alien invader is explicitly shown to be very fond of her, and will even put himself in harm's way to protect her.
%%* [[PetTheDog Pet The Cat]]: To Mr. Cat.
* SpoiledBrat - Throws tantrums if she doesn't get what she wants.
* {{Girly Girl With A Tomboy Streak}}: She definitely counts. While she's shown to have most of the same interests as Phoebe, such as playing dress-up and tea parties, but she's also shown to be quite violent, likes monster trucks as much as Coop does, and finds [[UglyCute Mr. Kat]] (an evil alien cat whom many people can't even tell is a ''cat'') to be cute.

[[WMG: Dennis]]
->Voiced by: Creator/CathyWeseluck

Coop's 10-year-old best friend, he is the one of the only people that believes Coop, their birthdays are only one day apart, and they always wish for the same presents. Dennis has black hair and black eyes.

* AbsenteeActor - He does not appear or is mentioned in Let The Games Begin, Me-Oh Me-Oh Meow, Flu the Coop, One Big Happy Family, Fishy Frisky Business, Fat Kat, Kat Whisperer, Under Destruction, Hit The Road, You Kat See Me, Mind Games, and Strange Kat On A Train.
* AmbiguouslyGay
* ButtMonkey
* ChasteHero: Has little to no interest in romance, and reacts with terror when flirted with.
** Interestingly enough, he is in a relationship with Phoebe in the alternate timeline.
* DeadpanSnarker - Whenever Coop goes too far off the deep end.
* GenerationXerox: Dennis' life is awfully similar to his dad's childhood.
* TheLancer: To Coop, who is TheHero.
%%* MissingMom- Subverted. She appear but unnamed.
* OnlyFriend: He's Coop's only real friend and stands by him. As such, he often does his best to help Coop stop Kat from his schemes.
* OnlySaneMan: Often tries to be this when things start escalating.
* RecurringCharacter
* SecondEpisodeIntroduction - He first appeared along with Lorne and Harley in Night of the Zombie Kat.

[[WMG: Burt Burtonburger]]
->Voiced by: Creator/TrevorDevall

Father of Coop and Millie Burtonburger. He is constantly stressed out due to Coop's "misbehaving". He owns the House of Swap. Burt has brown hair and black glasses.

%%* BumblingDad
* GenreBlind: Often why he's so oblivious to Kat's schemes.
* RepetitiveName: Seriously? ''Burt Burt''onburger?
* SitcomArchnemesis: He's this to Old Lady Munson and seems to have been this since ''he'' was a kid.

[[WMG: Old Lady Munson]]

->Voiced by: Linda Sorenson

A nosy old woman who is the next-door neighbor of the Burtonburgers. She is grumpy and mean to all the children and adults, though she favors Millie over Coop. She has a many greats-grand neice named Fiona, whom she tries to keep away from Coop.

* CrankyNeighbor: She's very irritable and foul-tempered to say the least.
* {{Jerkass}}: Especially to the Burtonburgers. Subverted with Millie.
* TheMunchausen - In "Down The Creek", when she tells plenty of fantastic stories to Millie. While Millie disregards them, the last shot is of pictures detailing this, implying Old Lady Munson was telling the truth.
* [[OlderThanTheyLook Older Than She Looks]] - You'd hardly believe that was possible, but it turns out she was already a crabby old lady when ''Coop's dad'' was a kid.

[[WMG: Phoebe Del Oro]]
->Voiced by: TabithaStGermain

A girl who has an unrequited crush on Coop and constantly annoys him. Phoebe clearly despise Millie (partially because Millie "owns" Kat and Phoebe owns Honeyfluff - an inferior, white-haired, obese cat). She has brown eyes, brown hair and brown skin.

* AbhorrentAdmirer: To Coop.
** AmbiguouslyBrown: Though her father seems to be Hispanic.
* RecurringCharacter/MinorMajorCharacter
* StalkerWithACrush: Phoebe can be less than subtle about her crush on Coop. After Fiona's appearance, she got [[{{Yandere}} worse]].
* {{Yandere}}: She's pretty terrifying when she wants to be.

->Voiced by: Creator/ChiaraZanni

Old Lady Munson's great great great great [[DepartmentOfRedundancyDepartment great]] grand neice, introduced in the second season. She is aware that Kat is an evil alien and Old Lady Munson tries to keep her and Coop apart. She has blonde hair and green eyes.

* ActionGirlfriend - She enjoys several sports and can easily keep up with Coop during fights against Kat.
* AffirmativeActionGirl: The first real girl we see get into action consistently.
* GreenEyes: One of her notable features.
* NotSoAboveItAll: While she's often the more level-headed and reasonable one, she can be as pig-headed and stubborn as Coop, which lead to a row between them.
* PluckyGirl: She becomes the third person to become aware of Kat being an alien invader and thus helps Coop out in stopping Kat.
* PromotionToOpeningTitles - After her first debut.
* WillTheyOrWontThey - With Coop
** TheyDo - They got married after the show.
%%* YouthfulFreckles