K-9 appears to be a green-furred martian-type dog. He is first seen in the Merrie Melodie sung by his owner, I'm a Martian. He is first shown in the song strapped up to create many other dogs. Then, he is shown sheepishly smiling while dancing with Marvin. His last appearance was his head floating downwards along with the martian rooster's head near the end of the song.
- K-9 was the first character to appear in a song, but not have any lines in it.
- K-9 also has the ability to talk and sing, as revealed in Laser Beam.