K-9 is Marvin the Martian's pet dog in Looney Tunes.
- Mario: K-9 and Mario never interacted.
- Chompy: K-9 and Chompy hate each other.
- Bowser Junior: K-9 likes Bowser Junior.
- Cody: K-9 attempted to eat Ken once, and they hate each other.
- Joseph: Joseph finds K-9 cool.
- Rosalina: K-9 likes Rosalina.
- Jeffy: K-9 hates Jeffy.
- Bowser: K-9 hates Bowser.
- Chef Pee Pee: K-9 eats the food Chef Pee Pee cooks, and they hate each other.