[[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
* TheCassandra - Nobody ever believes him about Mr. Kat.
* EnemyMine - Whenever a larger threat appears, such as Mr. Cheeks, Kat and Coop will work together.
* 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.
%%* TheHero
%%* MissingMom
* OnlySaneMan - He along his friend Dennis and later Fiona seem to be among the few well-adjusted folk in town.
* 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, it proves that Mr. Kat truly does like Millie.

* 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.
%%* {{Badass}}
%%* BrilliantButLazy
%%* ButtMonkey
%%* [[TheDogIsAnAlien The Cat Is An Alien]]
%%* CatsAreMean - Even alien-cats it seems.
* DevilInPlainSight - It's surprising how few people notice what he really is.
* 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.
%%* HairTriggerTemper
* RoboticReveal - "Nip/Duck" reveals that Kat is actually a cyborg.
* VillainousGlutton - He really loves cat food.

[[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
%%* BitchInSheepsClothing
%%* BlindWithoutEm
%%* DaddysGirl
* 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}}
%%* MissingMom
* 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.

[[WMG: Dennis]]
->Voiced by: 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.

%%* 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
%%* MissingMom- Subverted. She appear but unnamed.
* OnlyFriend - The only kid willing to consistently stay friends with Coop despite his obsession with defeating Kat.
%%* OnlySaneMan - Quite often

[[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
%%* RepetitiveName

[[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
%%* {{Jerkass}}
* TheMunchausen - In "Down The Creek".
* [[OlderThanTheyLook Older Than She Looks]] - You'd hardly believe that was possible, but yeah, apparently she is.

[[WMG: Phoebe]]
->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.

* AmbiguouslyBrown - Though her father seems to be Hispanic.
* 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. 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
%%* GreenEyes
* NotSoAboveItAll - She can be as pig-headed and stubborn as Coop, which lead to a row between them.
%%* PluckyGirl
* PromotionToOpeningTitles - After her first debut.
* WillTheyOrWontThey - With Coop
** TheyDo - They got married after the show.
%%* YouthfulFreckles