Jimmy Markum is a fictional character from the film Mystic River, directed by Clint Eastwood. He is portrayed by actor Sean Penn and is a central figure in the story, which revolves around the impact of a traumatic event from his childhood. As an adult, Jimmy becomes a tough and hardened man, dealing with the complexities of loss and revenge. In the film, Jimmy's life is deeply affected by the murder of his daughter, which leads him to seek justice. His character embodies themes of grief, loyalty, and the consequences of violence, making him a compelling figure in the narrative.