Arturo is a Mexican American adolescent adapting to life in a lower-income Los Angeles neighborhood after his family relocates from Mexico. He temporarily accepts the name "Arthur" to blend in at school before his grandmother's grief prompts him to reclaim his birth name. He speaks a blend of Spanish and English and plays the gourd in his older brother's garage band.

Papi is a steady, hardworking father employed at a local furniture store. He rarely raises his voice and conducts himself with old-fashioned manners, frequently removing his hat in restaurants and blessing his food. He drives a slow, restored Studebaker named Valentín and maintains a perfect attendance record at his job.

Mami is a dedicated homemaker who anchors the Rodriguez household with her constant care. She expresses her emotions primarily through her cooking, preparing complicated mole sauces when upset and traditional dishes to celebrate her family. She is characteristically gentle and prefers simple, strong bonds over flashy displays.

Arturo's paternal grandmother relocated from Aguascalientes, Mexico, following her husband's death. She wears traditional black clothing, speaks frequently with her late husband's spirit, and fiercely maintains her cultural practices. She cultivates a small corn plot in the yard to harvest huitlacoche, a traditional Mexican delicacy.

Luis is Arturo's high-school-aged older brother who possesses a natural passion for music. He plays the trumpet and forms a neighborhood band called Mega Mango, filling the local streets with loud, exuberant songs. He exhibits a more cynical, street-smart view of the world compared to his parents.

Rosa is Arturo's six-year-old sister who holds a deep affection for the color pink. She maintains an innocent, cheerful outlook on life and forms a pen-pal friendship with an older neighbor. Her sense of security relies heavily on her father's protective presence.

Alicia is one of Arturo's close classmates who experiences the pressure to Americanize her name. She joins Arturo in rejecting this forced assimilation, swearing an oath on Abuelita's molcajete to keep her true identity. She participates actively in their friend group's neighborhood activities.

Raúl is Arturo's classmate and friend who temporarily accepts an Anglicized name before reclaiming his identity alongside the group. He enjoys learning unusual vocabulary words and frequently intersperses Latin phrases into his casual conversations.

Jaime is another of Arturo's friends from the neighborhood who temporarily goes by an American name. He ultimately joins his peers in rejecting the change, remaining a consistent member of Arturo's core social circle.

Lloyd is a non-Mexican student who befriends Arturo and the others, earning the affectionate nickname "Rat Nose." He embraces his friends' cultural traditions, eats dinner at their homes, and actively participates in their group activities.

Miss Pringle is Arturo's well-meaning but culturally unaware school teacher. She assigns Anglicized names to her Mexican American students to make her own classroom management easier, largely oblivious to the emotional impact of her actions.

Leo is an older, white neighbor with a wiry beard who discovers the family's missing cat, Huitla, stuck in his avocado tree. Despite suffering from severe cat allergies, he keeps the pet safe and calls the family, leading to a warm neighborhood connection.

Coach Tree is a former NBA all-star who surprises the community by taking a job as the assistant basketball coach for the local school team. He accepts a nominal one-dollar salary, focusing entirely on mentoring the barrio's youth and teaching them discipline.

Ms. Cloud is the dedicated school librarian who fosters Arturo's love of reading by providing personalized book selections. She fights aggressively for better library resources, organizing car washes and pushing the PTA to improve the outdated catalog.

José is Alicia's brother and the star player of the local basketball team. He frequently causes trouble off the court and struggles with his reputation until Coach Tree takes a special interest in mentoring him.

Officer Paster is a local police officer who patrols the barrio. Unlike the apathetic response Arturo expects from law enforcement, Officer Paster demonstrates genuine sympathy for the family and takes personal action to help them feel safe again.

Flan is an older friend of Luis who drives a truck affectionately nicknamed Maybelline. He uses his knowledge of the Los Angeles streets to provide transportation for the younger boys' neighborhood activities.

Leona Scott, affectionately known in the neighborhood as "Mama Dulce," was a talented local piano teacher. She rejected fame to stay in the barrio and teach children music, happily accepting food and Mexican candy as payment for her lessons.