Ken is a 10-year-old boy who spends his summers at his family's Goose Bar Ranch in Wyoming. He possesses a highly active imagination that often distracts him from his chores, causing him to break equipment and frustrate his strict father. After failing the fifth grade, Ken seeks to prove his maturity by raising a young filly. He believes that having a horse to care for will help him become more responsible.

Rob is the owner of the Goose Bar Ranch and a strict former Army captain. He emphasizes respect, discipline, and hard work to manage the harsh financial realities of raising livestock. He values practical, easily trained horses over wild bloodlines, which causes friction when his son selects a difficult colt.

Nell is Rob's 37-year-old wife and the mother of Ken and Howard. Raised in Boston, she frequently notes the contrast between city life and her isolated daily responsibilities. She is an empathetic mother who advocates for Ken, successfully convincing her husband that giving the boy a colt might teach him the value of focus.

Flicka is a young, fast filly born into a line of difficult mustangs. She possesses a strong instinct for freedom, which makes her highly resistant to standard training methods. Her skittish nature requires immense patience and care to overcome.

Howard is Ken's 12-year-old older brother. He successfully manages his own horse, Highboy, and earns strong grades in school. He naturally aligns with his father's expectations, completing his ranch duties without complaint.

Gus is the Swedish foreman of the Goose Bar Ranch. He performs daily chores like milking cows and moving horses while acting as a steady, reliable presence for the family. He treats Ken with kindness and offers gentle guidance regarding ranch life.

Tim is a working ranch hand at the Goose Bar Ranch. He performs heavy labor alongside Gus, moving and breaking horses while occasionally drawing Rob McLaughlin's quick temper during stressful operations.

Rocket is an independent lead mare known for her incredible speed and refusal to be saddle-broken. She fiercely protects her offspring and regularly frustrates ranch operations by jumping fences.

Banner is the primary stud horse of the Goose Bar Ranch. He acts as a natural leader for the herd, using his discipline and commanding presence to stop stampedes and protect the mares.

Charley Sargent owns a neighboring ranch up north. He appreciates fast horses and partners with Rob McLaughlin to sell stock to a distant buyer.

Ross Buckley is a professional bronco-buster who visits the ranch to practice riding young horses. He relies on physical dominance to break horses and firmly believes that certain bloodlines are completely untamable.

Dr. Hicks is a veterinarian who travels to the Goose Bar Ranch to castrate the young colts. His efficient, bloody medical procedures shock Ken and represent the harsh realities of livestock management.

Joe Williams is a horse buyer from Colorado. He purchases unruly stock for auction and conducts his business with practical fairness, appreciating honesty from the ranchers he works with.

Dr. Scott is a medical doctor who serves the rural ranching community. He visits the Goose Bar Ranch to provide medication and care during times of severe illness, acting as an advisor to the family.

Albino is an all-white mustang and the grandsire to many horses on the ranch. Though he does not actively appear, his genetic legacy frustrates Rob McLaughlin, who blames the horse for the untamable traits found in his descendants.

Reuben Dale is a neighboring rancher. He shares information about local wildlife threats, specifically warning the McLaughlins about a dangerous mountain lion hunting in the area.

Highboy is Howard McLaughlin's personal colt. He is well-managed by the responsible older brother but requires daily grooming and attention to meet the strict standards of the ranch.

Rumba is a small, delicate three-year-old horse. Because of her physical size, she requires a lighter rider, leading the ranch workers to rely on Nell to gently train her.