Chance is an organic dog who lost one of her legs after being run over by a dog-sitter's boyfriend. She now resides at Dogtown, an animal shelter housing both living dogs and discarded robot pets. She holds special privileges within the facility because the human boss considers her a lucky charm for Wednesday night poker games. She observes her surroundings carefully, taking extra time to evaluate situations since moving requires more effort. She resents the robotic dogs, believing they lack hearts and take attention away from the organic animals.

Metal Head is an unusual robotic dog with a mismatched appearance, looking as though another dog's rear end is attached to his front. Unlike standard robot dogs that sit blankly until activated, he frequently ignores commands and actively searches through his user manual. He functions like a grieving organic dog, stubbornly holding onto the hope of returning to his former owner. He surprises the other dogs by actively learning and speaking dog language through sheer observation.

Mouse is a rodent who lives near the ceiling of the Dogtown basement. He communicates using sign language because he cannot speak dog or human languages. He relies on scraps of kibble from the shelter dogs to feed his extended family. He actively repays kindness, previously staging a stunt with playing cards that convinced the human staff to save Chance from euthanasia.

Management is the unnamed human boss who oversees operations at Dogtown. She manages a persistent lack of space and resources, placing highly adoptable dogs in prime locations while moving difficult or older dogs to the basement. She regularly makes practical decisions that favor the low-maintenance robot dogs over the organic ones. She hosts weekly poker games in the shelter and makes exception rules based on her personal superstitions.

Quinn is a young human boy who visits the shelter during designated reading buddy days. He struggles with traditional reading methods and ignores the organic dogs that perform tricks for his attention. He eventually forms a connection with a robotic dog capable of reciting books aloud to him.

Geraldine is a large, older organic dog residing at Dogtown. Due to her size and age, she struggles to attract the attention of human adopters who prefer young puppies. She provides comfort to the other organic dogs, offering gentle nuzzles when they feel sad. The shelter staff view her as a liability and target her for the euthanasia list.

Buster is a loyal golden retriever who lives at the shelter. He reacts strongly to perceived injustices against his fellow organic dogs, particularly regarding Geraldine's treatment. He organizes a group howl in protest of the staff's decisions, which earns him a punishment placement in the basement.

Jessie is the young human girl who previously owned Chance. Before a forced separation, she spent her days running and playing with Chance when the dog still had four legs.

Professor Besser is Jessie's mother and Chance's former owner. She took a six-month academic sabbatical that required her to leave Chance with a dog-sitter, initiating the tragic sequence of events that sent Chance to Dogtown.

Jimmy is the human boy who previously owned Metal Head. As he grew older, he became self-conscious about owning a robotic dog and viewed his pet as a toy suitable only for younger children, leading to Metal Head's placement in the shelter.

Marlene is a pampered Yorkie who enters the shelter system following the death of her human. She wears a leopard-print beret and fully expects her human to post million-dollar rewards for her return.