Mad Dog is the main antagonist of the episode "The Mask" of "Courage the cowardly dog".
The archetypical gangster, Mad Dog is the leader of a shifty gang of dogs living on the "wrong side of the tracks" (of an actual railroad track). He is narcissistic enough to believe his tattered apartment is first rate, and is willing to harm or kill anyone who challenges his way of life.
Because of this, his romance with his girlfriend Bunny isn't always functional, but he is smooth enough to coax her back into his arms every time. He keeps an over-sized flower pot in his living room. It was possibly used to torture his victims.