Anthropomorphic mammals.
While there are some standard humans (as noted in Valorum's answer), most of the people we see (aside from the primary cast) are humanoids with some vaguely canine features (the nose, mostly), rather than actual humanshumans:
There's Chief O'Hara (no relation) in the Mickey Mouse stories:
There's the Beagle Boys, of course (their dog-like noses are a bit more prominent than usual, probably tied to their name):
And, in the Barks and Rosa comics in particular, these same creatures tend to populate crowd scenes:
(These last two images from the Don Rosa story "A Matter of Gravity").