The Boy is an unnamed 12-year-old from Eden Prairie, Minnesota, who unexpectedly enters the business world. He possesses a strong moral compass and practical level-headedness rooted in his parents' teachings, though he struggles to grasp the complex economic systems he accidentally taps into. As his neighborhood lawn-mowing service explodes into a massive enterprise, he focuses on maintaining his work ethic while hiding his rapid financial success from his parents to avoid seeming boastful.

Arnold is an eccentric, honest stockbroker who looks and talks like he stepped directly out of the 1970s. He sports a bowl haircut, wears brightly patterned clothes with a poorly fitting suede sport coat, and frequently relies on outdated slang. Fascinated by the beauty of capitalism and grassroots entrepreneurship, he eagerly acts as a financial mentor, using his expertise to turn a small mowing profit into a diversified portfolio.

Joseph, who later adopts the catchy fighting name Joey Pow, is a local heavyweight boxer of humorous and enormous proportions. Despite his mountainous size, he moves lightly on his feet and possesses near-superhuman physical strength. He operates on straightforward, practical logic and demonstrates fierce, immediate loyalty to the people who back him financially.

The Boy's maternal grandmother appears erratic, speaking in a roundabout stream-of-consciousness that initially baffles listeners. However, her family understands that her seemingly disjointed logic eventually connects to deep, life-tested wisdom. She maintains a youthful spirit of adventure and proves highly supportive of her grandson's unusual circumstances as they develop.

Mom teaches at an experimental school and possesses the ability to do amazingly complicated mathematics in her head. She intentionally cultivates a light, stress-free atmosphere at home despite ongoing money struggles. She acts as a grounding force for her son, teaching him to prioritize compassion, mercy, and human decency over material wealth.

Dad is a freelance inventor full of ideas who tackles complex problems and deeply understands advanced physics concepts. His unconventional career means his income is unpredictable, and his experiments occasionally result in harmless household mishaps like the "Voice-Activated Door Incident." He handles setbacks with good humor and supports his family unconditionally.

Pasqual is a hardworking man who does yard work late at night, wearing a headlamp to see the grass while his wife watches their children. He recognizes The Boy's problem of having too much demand and connects him with a network of eager workers. He strikes a fair deal, asking only for a fifty percent split of the earnings in return for providing reliable labor.

Rock is a local gang leader who attempts to extort money from the workers associated with The Boy's expanding lawn-mowing enterprise. He targets the laborers with threats of violence, hoping to take advantage of their potentially vulnerable legal status. His intimidation tactics hit an immediate wall when he encounters the business's massive new protector.

Louis is one of Pasqual's cousins who joins the rapidly expanding neighborhood lawn-mowing operation. He works during the day to help manage the overflow of customers, representing the human element of the massive labor force that The Boy suddenly finds himself responsible for managing.