Mattie Ross is a fictional character from the novel "True Grit," written by Charles Portis. She is a determined and resourceful 14-year-old girl who seeks to avenge her father's murder. Mattie is characterized by her strong will and intelligence, as she navigates the challenges of the American frontier. In her quest for justice, Mattie hires Rooster Cogburn, a tough U.S. Marshal, to help her track down her father's killer, Tom Chaney. Throughout the story, she demonstrates bravery and resilience, showcasing her ability to confront danger and adversity in pursuit of her goals.