Mattie Ross is a determined, highly intelligent girl from Yell County, Arkansas. Narrating the story as an older woman looking back at her fourteenth year, she recalls how she refused to accept the bureaucratic delays of local law enforcement after her father was murdered. She relies on her sharp negotiating skills, unyielding religious morality, and stubbornness to force uncooperative adults to take her quest for justice seriously.

Reuben “Rooster” Cogburn is an overweight, frequently intoxicated US Marshal operating out of Fort Smith. Missing an eye and harboring a dark past as a Confederate guerilla fighter, his law enforcement methods are brutal and often legally questionable. Despite his rough exterior, cynical attitude, and tendency to solve problems with violence, he accepts Mattie's bounty to track her father's killer into the Indian Territory.

Tom Chaney, who also goes by the alias Theron Chelmsford, is a drifter with a distinctive dark mark on his face. After being hired out of pity to work on the Ross family farm, he repays the kindness by shooting Mattie's father during a dispute over gambling losses. He is a resentful and careless man who steals his employer's horse and money before fleeing into the lawless Indian Territory.

LaBoeuf is a proud, well-groomed Texas Ranger who is tracking Tom Chaney for a lucrative bounty. He carries an expensive Sharps rifle and exhibits a vanity that frequently annoys his traveling companions. He insists on taking the fugitive back to Texas to hang for killing a state senator, putting him at immediate odds with Mattie's plans for local justice.

Frank Ross is a kind-hearted farmer and Civil War veteran from Yell County, Arkansas. His decision to hire a drifter out of pity ultimately costs him his life when a drunken dispute turns fatal. His death leaves his family in a precarious financial situation and serves as the catalyst for his daughter's vengeful journey.

Colonel Stonehill is a businessman and horse trader in Fort Smith who suffers from annual bouts of malaria. He severely underestimates Mattie's intelligence and finds himself outmaneuvered by her aggressive negotiation tactics regarding her late father's property.

Lucky Ned Pepper is a notorious outlaw gang leader operating in the Indian Territory. Having recently robbed a train, he and his gang are currently on the run, making him a prime target for federal marshals while reportedly harboring the fugitive Tom Chaney.

Lawyer Daggett is the Ross family attorney residing in Yell County. Though he is not physically present in Fort Smith, his name is frequently weaponized by Mattie as a threat to force adults into legal compliance.

Yarnell Poindexter is a farmhand who works for the Ross family. He accompanies Mattie to retrieve her father's body, serving as a brief voice of caution before returning home alone.

Mrs. Floyd is the nosy and talkative proprietor of the Monarch boarding house in Fort Smith. She provides lodgings to Mattie and offers unsolicited advice and medicine when the young girl falls ill.

Grandma Turner is an elderly blind woman living at the boarding house. She notoriously steals the blankets during the night, leading to a frustrating sleeping arrangement for her young roommate.

Judge Isaac Parker is a stern legal authority who presides over the federal court in Fort Smith. Known for sentencing criminals to death, he attempts to bring order to the neighboring territories by employing ruthless marshals.

Lee is a Chinese merchant who operates a general store in Fort Smith. He allows his friend to live in the back room of his shop and frequently spends his evenings playing cards and selling ammunition.

Odus Wharton is a criminal standing trial for murder in Fort Smith. He holds a deep grudge against the marshal who arrested him following a brutal shootout that left his father and brother dead.

Quincy is a small-time crook hiding in a valley shelter. He is highly suspicious of law enforcement and fiercely determined to keep his wounded partner from sharing valuable information with the marshals.

Moon is a young criminal suffering from a severe leg wound at the dugout shelter. Under intense interrogation pressure, he contemplates trading his knowledge about outlaw movements for medical assistance.

Captain Boots Finch is a commander of the law enforcement division that polices the Indigenous territories. He acts as a friendly colleague, providing essential updates on outlaw movements and participating in shooting contests.

Haze is a criminal riding with a notorious outlaw gang in the Indian Territory. He participates in train robberies and attempts to evade the federal marshals hunting his crew.

The Original Greaser Bob is a Mexican bandit riding with a wanted gang. He is noted for performing acrobatic horse-riding tricks to avoid gunfire during shootouts.

Potter is a deceased US Marshal and former Civil War comrade. He worked closely alongside his partner until suffering a mortal wound during a violent law enforcement raid.

Blackie is a sturdy and reliable pony purchased in Fort Smith. The horse is bought specifically to carry its young rider into the rugged and dangerous Indian Territory.

Judy is a fine horse belonging to the Ross family. The animal is stolen into the Indian Territory immediately following a fatal shooting, prompting a pursuit across the border.