Cat King is the King of Cats. He's distinguished from his subjects in that he's the only red one, has a different body pattern, and is slightly bigger than other cats. He's one of the few animal leaders that's capable of human speech.
He, like all the other cats, was overtaken by the misery caused by the hairballs in their stomachs. This made him hate the sound of the laughter and he had his minions procede to punish the humans and anyone else who laughed in his kingdom.
In "Cat Castle", he heard the humans laughing so he and his minions through their Chili Powder firecrackers on them which made the humans' eyes burn. Later the Zebras came and ordered him and his subjects to attack Big Green but they laughed while saying it and this made the cats fire their bombs and take them hostage. Later ApeTrully and the Tank Army arrived to make peace but he found that the cats took the Zebras hostage. He then made a cat joke and laughed which made the cats angry. They bombed him and took him hostage too. When First Squad shows up they find that the Tank Army is suffering from the chili firecrackers and then together devise a plan. At night they trick the cats into a machine (which in turn could be the Skywheel Tank) that makes them dizzy and then tie the cats up. Mighty Ray, with help from the rest of First Squad, makes them laugh and cough up their hairballs. Grateful for returning happiness to them, Cat King joins Big Green where he and some of his soldiers help Mighty Ray with his comedy act.
In "Fireworks Festival of East Citadel", he's one of the contestants for the competition. The Cats' tears act like acid.