Original Appearances: Looney Tunes cartoon “Hardevil Hare” (July 24, 1948).
Other Appearances: Also the Looney Tunes cartoon “The Hasty Hare” (1952), as well as comics, games, and guest-appearances in Looney Tunes: Back in Action and two episodes of Duck Dodgers (where he's identified as Commander K-9).
Biography: We don't know for sure when Marvin the Martian acquired Commander K-9. In fact, we don't really know for certain that K-9 is truly a pet, or if he's actually considered to be a subordinate to Marvin (given his clothing, that's a possiblity).
Powers: None that have been demonstrated.
Group Affiliation: If Marvin's part of some kind of Martian militia, K-9's likely part of it, too.
Miscellaneous: K-9 was missing from three of the five original cartoons with Marvin the Martian. Despite his relatively rare appearances, he's been featured in loads of merchandise!