Quite opposite of his carefree and calm-tempered creator Madame Foster, Mr. Herriman is a stickler for rules, having made many silly and impractical rules in an attempt to keep everything "running smoothly," to the point of being ridiculous. Throughout the series he has shown a lot of symptoms of having OCD when it comes to cleanliness and following the rules perfectly. He usually refers to others in a proper manner, calling males "Master" and females "Miss" in front of their name, the only time he actually calls people in normal fashion is when he is in pure terror. He sets great store by "proper manners," and is rarely seen acting on his primitive rabbit nature. He is shown to have an addiction to carrots (which he will go to great, even desperate, lengths to hide), despite his best attempts to ignore or get over the weakness.
He is phobic of dogs and is easily sent into a panic whenever he comes across a dog or anything dog related which is why he made a rule that no dogs are allowed in the home, which causes problems for him when a litter of imaginary puppies arrive in the house. He is frequently called a "badger" who one who looks like Bugs Bunny by Goo, throughout the show (until the episode "Bus the Two of Us"). Mr. Herriman, though proper, has often shown a lack of social skills. His ways of being proper are to the point to where the other imaginary friends cannot stand him or being around him, his ways of keeping things "running just the right way" often inconveniences the other characters to the point of being disrespectful. Frankie has a strong disliking towards Mr. Herriman, due to his constant lack of consideration towards her and often talks her down, whether he is aware of it or not.
At the end of "Destination Imagination", however, he realizes his poor judgement towards her after witnessing how she handled World, even putting forth an agreement to have the other friends help her around the house. He has a strong disliking for Bloo, due to his chaotic nature and constant rule breaking. However, we discover in "Let Your Hare Down" that he has a laid-back alter ego named "Hairy", who wears a Cat in the Hat stovepipe hat, star-shaped sunglasses, his moustache in braids and looks like a hippie. Although Mr. Herriman is a strong stickler for the rules, he is often over-ruled by his creator Madame Foster.
Despite the fact that they often disagree on things (rules mostly), Herriman and Madame Foster have an unquestionably loving relationship, and at time Herriman will appease his creator much in the way that he did when Madame Foster was a little girl (such performing his 'Funny Bunny' dance and song for her when in private). He is also very protective of Madame Foster, to where even she tells him to relax. Mr. Herriman is very passionate about his job as the house president, taking the job seriously, as he's stated that being the president of the house makes him feel like he is needed and important to the Foster community. Herriman is surprisingly old fashioned, even believing that the internet is an actual net. It is believed that Madame Foster created him during the 1930s, making him believe the 2000s are still running in the old-fashioned ways of living.