Wolf

Wolves almost always travel in packs. Though they are less numerous than the horrible mongrels in Dogtown, wolves are much more individually dangerous and persistent. Wolves have sharp teeth and will frequently knock a target over, then attack the head.

Van Buren
One of them lives in the Nursery Repository, and can be acquired as a follower.

Physical attributes
Unlike other Wasteland creatures wolves seem to have been barely (if at all) affected by radiation which makes them one of the few "unmutated" animals still living in the wastes.

Fallout: New Vegas

 * Do they actually appear in New Vegas? I've been all over the map and haven't seen one yet. I saw something akin to a Fallout 3 Scavenger Dog once when my game glitched when I exited Helios One but I've never seen one while playing the normal game, just a lot of Coyotes. - Pisterator