Mattie is smart, talkative, and nearly fearless, at least when it comes to arguing with adults. She has an impressive vocabulary and peppers her speech with legal terms and references to the Bible. Although Mattie is precocious, she also has no discernment with which to modulate her personality, acting like a kid one moment and like an adult the next. She is the same with everyone, never adapting her style to conform. As a result she often says odd, unfitting things, such as inviting two saddle-weary lawmen to tell ghost stories with her, or recommending her lawyer to a ruthless criminal. Mattie is certain of her judgments: cats are evil; Chaney is a "worthless Louisiana cur"; gentlemen who do not rise from their seats in her presence are "trash." She is therefore surprised by Rooster and LaBoeuf, who continually reveal different facets of themselves to her.
The sheriff describes Rooster as the meanest of the three best federal marshals available; he is also hard-drinking and dissolute. He often ignores the regulations that come with being a marshal, back-dating his expense accounts. His testimony under cross-examination in the trial of Odus Wharton reveals he is somewhat cavalier about legal and ethical procedures, perhaps moving a dead body to create a better crime scene, or shooting a man in the back to get the drop on him. However, he does have "true grit," as Mattie says. He has the bravery to ride straight at four opponents, daring them to flinch. Before becoming a lawman, Rooster was an outlaw. In the Civil War he rode with Quantrill's Raiders, a group of Confederate irregulars who harassed and pillaged towns suspected of Union sympathies. After the war, facing arrest for his activities with Quantrill, Rooster and Columbus Potter rob a Union Army paymaster of $4,000 to get a stake for their next start in life.
LaBoeuf is vain; he clanks around in his spurs indoors, and he wears his hair in a cowlick Mattie suspects is deliberately styled. He tells Texas Ranger legends and he gets angry when he suspects Rooster is trying to "make me out foolish in this girl's eyes." However, LaBoeuf proves himself a good shot and a loyal friend.
Tom Chaney's real name is Theron Chelmsford, and he is from Louisiana. He is wanted for killing a senator and his dog in Texas, so he was already a criminal when he showed up at the Rosses' farm, posing as an honest man down on his luck. Chaney's most distinct physical feature is the black mark on one of his cheeks. The mark was left by gunpowder when a man shot him in the face. Being shot in the face seems typical of the feeling Chaney inspires in others. His most distinct character trait is his self-pity. Although he caused his own troubles by shooting the unarmed Frank Ross, he complains, "Everything is against me."