Mac actually belongs to Dr. Gordon, the owner and primary veterinarian of All Cats. He is one of the two diabetic in house cats. You may notice Mac's picture shows only one eye; this is because Mac had an eye removed due to his diabetes. He enjoys sleeping in the lobby most days, running to hide only when his internal clock reminds him that someone will be coming to check his blood sugars and inject him with insulin.
Due to Mac's irritability when disturbed from his pleasant dreams, he earned the title of The Grumpy Old Man. He will growl to inform you that he is annoyed and has even been known to bite you if seriously provoked.