Bull is smaller and has a bluish color. He acts as the leader and the "brain" of the duo. Axle on the other hand is taller and acts very stupidly, although he does demonstrate knowledge or has good ideas sometimes. Whenever Axle acts smart, Bull will remind him that he's the sidekick and thus is supposed to be stupid and Axle will cheerfully apologize and act stupidly, even though he knows Bull will often beat him in the head for his stupidity. Despite this violent behavior, they are both very soft-spoken and calm and appear to be best friends. In one episode, Axle reveals that he has doctorate, PhD and master's degrees in several fields of knowledge and is actually very smart, but voluntarily chose to work as a dumb sidekick because it made him feel livelier.
They are extremely similar to a later and much more famous Warner Brothers cartoon duo: Pinky and the Brain, with Axle and Pinky even sharing the same voice actor, Rob Paulsen. Bull on the other hand is voiced by John Astin. Axle also made a very brief cameo in an episode of Duck Dodgers called "MMORPD"