He is voiced by Kathleen Barr.
He is a cat-like alien from a distant planet called Catnip and his species are called Katnipians. He was sent down to Earth to collect a brand of cat food called Fishy Frisky Bits and give his companions a chance to take over Earth, because his planet is so polluted that its inhabitants need to colonize a new one. Kat's physical appearance can be likened to that of the hairless Sphynx cat. He has a cybernetic body and numerous superpowers, such as steel claws, heat ray, heat emanation, heat vision, intelligence, acid spit, claw blades, steel fangs, pulse manipulation, extendable tail, mold, x-ray vison, super strength, defy gravity, invulnerability, and super speed. Kat is also shown to put on weight very quickly whenever he consumes food with fattening properties. Cat food seems to have no weight effect at all. Just like the cats on earth, he hates water and baths.
At first when Millie asked her father if they could adopt the strange-looking animal (supposedly a cat), Burt turned her down, stating that it had a collar on and therefore probably had an owner. He was forced to compromise though, when his daughter threw a tantrum, deciding that she could keep Kat if and only if they couldn't find it's owner.
He was sent to earth mainly to gather Fishy Frisky Bits for his home planet, however he has also planned to take over the world. Kat extremely hates Coop, who usually foils his plans. Coop and Dennis are the only characters on the show who know Kat by his true self, while everyone else sees him as a hideous but normal creature (similar to the Dib and Zim relationship). This provides Kat the opportunity to do things that Coop is usually blamed for afterwards. However, he has occasionally teamed up with Coop and Dennis when his plans go awry.
Kat also seems to dislike extremely reckless chaos though this purely down to not wishing to be discovered, this is most prominent in his confrontations with Mr. Kitten - his rebellious teen son.
Kat is also the focus of intense bullying by his superior Kat Kommander, who frequently harasses him via holographic displays and berates his many "failures".
- Indestructible Claws: Kat has almost indestructible claws that can break just about any material. They are so strong that the vet needed a diamond tipped cutter to clip them, and even then the cutter was ruined, even though Kat was able to resharpen them easily enough. This is Kat's most common attack against Coop. He has also been known to shoot lasers from them and weld with them, it is unknown if they are shiny enough to focus light or because of his cybernetics. Probobly the latter because he has been shown to do this indoors,
- Heat Ray: Kat uses this ability to create a ray of heat. With this ability he can melt almost any object.
- Heat Emanation: The power to produce heat from his claws. He uses this to melt the ice, steel, iron, about anything.
- Ocular Heat Emanation: Same as heat emanation but from his eyes. Kat commonly and always uses this to show off how angry he is and how much rage he is feeling.
- Superior Intellect:Kat possesses superior intellect as shown in "Dial B For Babysitter" where he plots a plan against Old Lady Munson, but it was later revealed in the episode he was only trying to contact other Kats in space. He also has TWO extremely advanced brains.
- Acid Spit: Can spit acid, in the form of a hairball, to burn though anything. As seen in "Class Act", he uses it to gain access to the vet at night. In addition, Kat also uses his acid spit to attack Coop and in his experiments in "Planter's Warp". Kat use acid spit in "One Big, Happy Family" to gain access to the room the Burtonburgers are trapped in to torture Coop while he is told to stay on the stool. In "Nip/Duck", Kat is shown to have a machine inside his throat, so his acid saliva probably comes from that device. Other kat's spited acid in "Kat to the Future Part Two".
- Claw Blades: His claws can also change into buzz-saws.
- Titanium Fangs: Kat possesses five rows of razor-sharp serrated fangs made out of titanium that can break through most Earth metals and even the toughest material in the universe, durasteel; one example is when he bent the hockey net Coop was guarding during "Play N'Ice". Another time is when he goes crazy in the episode "Trespassers Will Be Persecuted]", because he has been eating catnip; if you notice in the episode, he actually bites off a piece of Old Lady Munson's gnome.
- Pulse Manipulation: The power to make a pulse, even though he hasn't got one; it is unknown how he is able to do this, but it's probably thanks to one of the machines he has inside his body.
- Extendible Tail: The power to extend his tail to any length and manipulate it like another limb. Kat also uses his tail sometimes as a lasso. One obvious hint of this power is that Kat's tail is mostly curled up during the show; this proves it has the ability to extend outward.
- Shapeshifting: One advantage that Kat uses all the time is that he doesn't have any hard parts in his entire body at all, just muscle, and the power to change into any shape or form without injuring himself. Kat used this ability on countless occasions, usually to break into a building, or even to break out of something.
- X-Ray Vision: In Special Christmas 2/2, Kat uses X-ray vision to see which present holds the Captain Blasteroid Rocket Ship. It is unknown whether he can use X-ray vision in both eyes or just the left one as we only see him use his left eye in the episode. This proves that he is indeed part cyborg.
- Super Strength: Seen in "Nip/Duck", Kat holds Dennis ransom by holding his dad's piano above him (while Dennis is sleeping) in exchange for his X-rays.
- Defying Gravity: Kat has the ability to defy gravity and walk on the ceiling; this is seen in a couple of episodes, usually while Coop and Kat are alone (otherwise people would get suspicious that a cat is walking on the ceiling). It is unknown why Kat can walk on the ceiling; it is probably due to his razor sharp claws or it could be he just has the ability to do this.
- Kat's Blood: Kat's blood has the ability to mutate certain creatures that come in contact with it. It is unknown why Kat's blood can mutate creatures but is probably due to the fact that Kat is part cyborg so his blood probably has a mutating agent inside it (like toxic waste).
- Invulnerability: Kat can take punishment which could seriously injure if not kill a normal cat let alone a human with considerably less damage. In "Trick or Threat" you can see Kat run right into a fence and break it without suffering any damage to himself. He has also survived very many burns and shocks that would put a human in the hospital!
- Gliding: Kat has shown to have the ability to glide, like that of a flying squirrel.
- Walking on Water: Kat can walk on the water.