Alec is a fair-complexioned, red-headed schoolboy from New York City with a deep love for horses. Raised in a polite and structured environment, he possesses a resilient and adventurous spirit that surfaces during a crisis at sea. His unique bond with an untamed horse tests his courage and forces him to take on serious responsibilities.

The Black Stallion is an exceptionally large, muscular, and untamed horse with the appearance of an Arabian but far greater size. He views almost all humans and other animals as immediate threats. Despite his highly aggressive disposition, he shows a unique and selective tolerance for a young boy who offers him sugar cubes and quiet companionship.

Henry is a plump, retired championship jockey who recently purchased the property next door to the Ramsay family. He maintains a wealth of knowledge about racehorses and clearly misses his active days on the track. Recognizing extraordinary physical potential in his young neighbor's animal, he eagerly provides stable space and professional guidance.

Napoleon is a 15-year-old draft gelding who pulls a merchant cart through the busy streets of New York City. He is thoroughly docile and unbothered by the aggression of wilder animals. He serves as a grounding presence and a strictly necessary companion for his highly anxious stablemate.

Mr. Ramsay is Alec's father, living in New York City. He shares a baseline appreciation of horses with his son and brother, but approaches Alec's sudden responsibilities with parental caution. He requires Alec to maintain excellent grades in exchange for keeping his demanding new pet.

Mrs. Ramsay is Alec's mother. She is a comfortable, middle-aged woman who worries deeply about her son's physical safety after believing he was lost at sea. She struggles to understand the intense bond between Alec and his imposing animal, preferring to stay entirely out of the barn.

Uncle Ralph is a missionary stationed in India. He hosts his young nephew for a summer vacation and spends considerable time teaching the boy how to properly ride and handle horses, inadvertently preparing him for his upcoming survival trials.

Tony is an energetic street merchant who works the neighborhoods of New York City. He stables his draft horse in Henry's barn and is initially terrified by the sudden presence of a massive, aggressive animal in the adjacent stall.

Mrs. Dailey is Henry's wife, a practical woman who helps manage their newly acquired residential property. She grants Alec provisional permission to use their empty barn, provided he puts in the labor to clean it up first.

Jake is an elderly gatekeeper at the Belmont Park racetrack. He is a former horse trainer who mentored Henry years ago, and he maintains a deep, professional appreciation for pure equine stamina and power.

Joe Russo is a newspaper reporter operating in New York. He possesses a sharp eye for an interesting human-interest story and readily trades transportation favors for exclusive interviews about Alec's shipwreck survival.

Jim Neville is a prominent New York City sports columnist. He holds significant influence in the racing world and strategically uses his newspaper platform to stir up public interest in potential matchups on the track.

Whiff is one of Alec's regular school friends. He is easily intimidated by large animals and vastly prefers to watch safely from a distance while Alec interacts directly with his horse in the pasture.

Bill is a local classmate of Alec's. Like Whiff, he is completely overwhelmed by the sheer size and ferocity of Alec's animal and relies heavily on conventional track wisdom when discussing racing champions.

Pat is an Irish sailor working aboard the cargo ship that responds to a massive signal fire on a deserted island. He is highly practical and observant, quickly noting the potential financial value of the dangerous animal they hauled aboard.

Cyclone is a highly celebrated thoroughbred racehorse. Known universally as the champion of the East Coast, he is brought to Chicago to compete in a highly publicized match race designed to definitively crown the fastest horse in the country.

Sun Raider is a massive, formidable racehorse shipped in from the West Coast. Almost as large as his wildest competitors, he possesses a deeply aggressive streak and proves to be a fierce physical challenger on the track.