Sylvester Junior is the son of Sylvester the cat in the Looney Tunes cartoons. Essentially Junior is a chibi, looking just like a pint-size version of his old man, and having a large head in proportion to a small body. His first appearance was Pop 'im Pop directed by Robert McKimson. Mel Blanc voiced both father and son.

Mckimson gave Sylvester a blustering, braggart personality in his pictures, frequently talking about his youthful exploits catching mythical giant mice. Junior often wishes aloud that a giant mouse would materialize right that minute. Sylvester says that there are no more, implying he defeated the last one year ago. Later the fabled "giant mouse"--Hippety Hopper--will appear. In "Pop 'Im Pop!" the mouse escapes from a circus, makes trouble hopping around town, and ends up cofronting the cats. Sylvester, after being whalloped a few times, chases the mouse into the circus tent. To save face with his boy, begins to yell threats at the absent mouse, and says he wishes the mouse were twice as big with multiple heads and arms. He gets his wish--Hippety, in his very annoyed mother's pouch, emerges. Sylvester, suddenly a craven again, grins and beats a hasty retreat--followed by Junior. Hippety, ever playful, waves bye-bye.

Tweet Dreams was the only classic pairing of Junior and Tweety. Hippety appeared in a Sylvester and Tweety Mysteries cartoon (Sylvester exclaims at one point he hadn't seen giant mice in years!) set in Austrialia...and Junior appears in "A Mynah Problem", in a flashback sequence to his childhood, which the spittle-spraying cat has upon his failure to capture the Chuck Jones hopping mynah.