Agnes Harper's tabby, William, is the oldest of the 5 toms in the fictional neighborhood. But being a multiple cat owner, I have learned that seniority doesn't necessarily ensure a top position in the feline hierarchy. William doesn't particularly care for Kaiser the German shepherd K-9 officer, but I didn't want them to be completely at odds. Hence, the need for a contentious Siamese mix. Meet Mao, a bigger, younger male in the neighborhood.
Four-legged characters are really fun to create. I try not to anthropomorphize them too much, and that can be a challenge. Personally, I don't think we give other species near enough credit when we consider their intelligence and sensibilities.
Cats are very territorial, having clearly-delineated boundaries to their areas. Throughout the story, William is on a mission. Unfortunately, the mission leads him into Mao's domain with fur-flying results. This altercation is witnessed by the well-disciplined Kaiser, who leaps into the fray. Kaiser's involvement proves to be essential to the main story line.
So far, this is the cast of nonhuman characters. Who knows? Maybe some more will develop, adding to the fun!