Benji is an affluent seventh-grade student who acts as the class clown to mask his insecurities. He plays center on the basketball team but lacks natural talent, feeling immense pressure to live up to the athletic legacy of his parents. When he discovers a lost wallet in Central Park, he impulsively spends the cash inside, initiating a massive financial challenge. He initially views wealth as an easy tool to buy popularity and secure social standing among his peers.

Felix is a cautious, rule-following seventh-grader who lives with his single mother in a small, one-bedroom apartment. Accustomed to tight budgets and financial scarcity, he brings a modest peanut butter sandwich on the field trip and feels intense guilt after Benji uses money from a found wallet. He approaches the billionaire's challenge with anxiety, meticulously calculating daily spending requirements while trying to hide his newfound wealth from his struggling family.

Laura is the eccentric tech billionaire who founded the social media platform Friendly Connect. After losing her red leather wallet in Central Park, she decides to teach the boys a harsh lesson about accountability. Instead of a standard reward, she locks them into a strict legal contract requiring them to spend over five million dollars in thirty days, viewing the exercise as both a moral punishment and an entertaining experiment.

Karen is Felix and Georgie's single mother. She works extra shifts at a nursing home and a warehouse to support her family, enforcing strict rules about money out of absolute necessity. Unaware of the spending challenge, she attempts to plan for her family's future on a severely restricted budget, creating tension when Felix begins spending lavishly.

Jack is Benji's father and a former high school basketball star. He lives in a large, comfortable house and provides his family with financial security. He places heavy athletic expectations on his son, desperately wanting Benji to continue the family legacy on the basketball court.

Benji's mother is a former college basketball scholarship recipient. She frequently checks Benji's homework and monitors his digital journal, expecting him to maintain high academic and athletic standards. She casually hands out twenty-dollar bills when asked, demonstrating her insulation from financial hardship.

Reggie is a 22-year-old philosophy student at the University at Albany who works as an Uber driver. Benji hires him for a thousand dollars a day to serve as the boys' personal chauffeur during their challenge. He frequently offers academic observations about the boys' choices, applying concepts like determinism to their rapidly escalating spending habits.

Alma is a principled classmate of Benji and Felix. She consistently declines Benji's attempts to provide free food to the school, preferring her own packed lunch. She questions the ethics of the boys' sudden excessive spending, challenging Benji to find a more meaningful use for his resources.

Georgie is Felix's older sister who works at Downtown Donuts. She is engaged to her partner, Michelle, and hopes for a beautiful wedding that her family currently cannot afford. She remains largely unaware of the exact nature of Felix's sudden access to money.

Aidan is a middle school student who consistently targets Benji and Felix. He cruelly mocks Benji's lack of athletic skill using the nickname "Barney" and physically steps on Felix's sneaker to cause him to fall. He opportunistically changes his attitude, demanding favors when he realizes the boys have money.

Freebie is a scrawny, matted stray dog that Felix discovers during a morning drive. Felix immediately bonds with the dog, using challenge funds to pay for extensive grooming and veterinary care. The dog becomes a constant companion, offering the boys a sense of unconditional loyalty.

Leonard is the accountant hired by Laura Friendly. He sets up the boys' shared banking app and strictly monitors every transaction, holding the power to approve or reject purchases based on the challenge's rigid legal rules.

Roger is Laura Friendly's lawyer. He is responsible for drafting the strict non-negotiable contract that governs the boys' access to the five million dollars, ensuring the parents have zero control over the funds.

Tracey is Laura Friendly's assistant. She handles the logistics of the billionaire's sudden appearances and manages the immediate details of the boys' initial meetings with her boss.

Ms. Chenoweth is the boys' seventh-grade homeroom teacher. During the field trip to New York City, she repeatedly warns Benji to stop wandering off and eventually helps the boys hand the found wallet over to a police officer.

Michelle is Georgie's fiancée. She is supportive of the Rannells family and looks forward to her upcoming wedding, gratefully accepting the extravagant pre-honeymoon trip the boys organize to Disney World.

Mark is Felix and Georgie's estranged father. He has not seen his son in years, leaving Felix with deep-seated anxieties about whether his father will only return to their lives because of the money.