Jack is an Oggy's Cousin Green Cat and the deuteragonist (in a few episodes an antagonist) of the show. Like Oggy, he fights the Cockroaches.
He is an olive green cat with a red nose, pointed ears with hairs coming out of them, and a big head.
Jack can be easily described as the opposite of Oggy. He's aggressive, focused, short-tempered, sometimes lazy, obnoxious, and mechanic. More often than not, he's focused on getting rid of the cockroaches or doing something selfish. Jack often builds something to try and destroy the cockroaches, or any other insect that roams Oggy's house—and while he has had some success, more often than not his plans backfire. He also sometimes bullies Oggy, either moving him when he's in front of the TV, trying to beat Oggy in a race, or just going plain insane. He is perhaps the easiest target in the show, mainly because his rage gets him too unfocused on either getting rid of the cockroaches.
However, at times, Jack can show his nicer side when he's not focused on stopping the cockroaches or acting villainous. He tends to play the "straight-man" to Oggy and the roaches' antics.
- Jack will get seasick if he goes on a cruise ship, as shown in "Mayday! Mayday!".
- Jack is known to have aerophobia in "The Lighthouse Keeper", yet he isn't afraid of them when flying airplanes.
- Jack is shown to be afraid of monsters in "Monster from the Mud Lagoon".
- Jack, being Oggy's cousin, could very likely reference the real-life shop Cousin Jack's Pasty Co., where it sells cornish pasties, and "oggy" is also an alternate name for cornish pasties.
- In Mayday! Mayday! Jack is revealed to be seasick. However, in Castaway Cats he never shows any signs of being seasick.
- Jack's residency is inconsistent. In some episodes, he lives in his own house and usually visits Oggy, while in other episodes, he'd be roommates with Oggy. This has stopped in Season 4, where Jack has been given a permanent house.
- Then again, being from a comedy show, this inconsistency might be for comedic purposes.
- Even though Jack's home is next to Oggy's, he'll always ride in his jeep instead of walking.