K-9 is a green cartoon Martian dog in the Warner Brother's Looney Tunes series of animated shorts. He is closely associated with Marvin the Martian as K-9 is Marvin's pet dog and sidekick in some Looney Tunes productions. He has a few resemblances to Disney's Pluto.
K-9 premiered in the short Haredevil Hare, where he and his owner Marvin tried to thwart Bugs Bunny, who had stumbled on the pair's plans to destroy the Earth. He is given his first speaking role in this short, seeming quite unintelligent and gullible. That changes in later shorts where K-9 carries an air of superiority over his owner.
He has a starring role in two episodes of Duck Dodgers: "K-9 Quarry" and "K-9 Kaddy", in which he saves his master from dangers, and is berated by an oblivious Marvin, in a similar manner to the Porky and Sylvester shorts. The second of these episodes set him against Martian versions of the Goofy Gophers, in an obvious reference to Pluto's adversarial relationship with Chip N Dale.