James Cat (voiced by Jim Cummings) and Thomas Dog (voiced by Tom Kenny) are the main characters of CatDog. They are two animals that were conjoined together.
Cat is the more smarter and cunning of the two, but he can also be greedy, mean and selfish. But he's also good-hearted, intelligent and likes reading, gardening and enjoys listening to classical music. Despite his sophisticated personality, Cat has a dark side. When he snaps, Cat becomes a ruthless, psychopathic manic whom even The Greasers are scared of, once they see what he is capable of.
Dog is the more happy-go-lucky and more naive of the two. He's also the sorce of clumsiness. He is quite gullible and will believe anything he's told. His attention span is short and is distracted by balls, garbarge trucks, food, bones and his overactive imagination. Because of his simple nature, Dog usually is the one that gets him and Cat into trouble. Not paying any attention to Cat's warnings, his actions always gets them into much bigger trouble. Despite this, he's the more popular and athletic of the two. Much to Cat's dismay since he's a neat freak, Dog leaves a mess everywhere he goes. Dispite all of this, he's quite friendly and loyal.
- CatDog will meet Jeffrey and his team in Jeffrey & Friends' Storm Adventures of CatDog: Fetch.
- CatDog will meet Craig and his team in Craig & Friends Adventures of CatDog: Quest for the Golden Hydrant. At the end, CatDog will join the club.