Briony Tallis is a fictional character from the novel "Atonement" by Ian McEwan. She is introduced as a young girl with a vivid imagination, who aspires to be a writer. Her actions and misunderstandings lead to a pivotal event that dramatically affects the lives of those around her, particularly her sister Cecilia Tallis and Robbie Turner, a family friend. As the story progresses, Briony matures and grapples with the consequences of her childhood decisions. Her journey reflects themes of guilt, redemption, and the complexities of human relationships, making her a central figure in the narrative's exploration of atonement.