John Hancock is a seemingly invincible superhero living in Los Angeles, who possesses immense strength, speed, and the ability to fly. However, his anti-social behavior and alcoholism have led to a significant amount of collateral damage in his attempts to fight crime. His recklessness and disregard for property make him a pariah in the community, and he is disliked by the general public and the authorities. Despite his efforts to do good, his actions often result in costly destruction and a negative public image.

Ray Embrey, a well-intentioned public relations executive, is saved by Hancock during a train accident. Ray believes he can restore Hancock's public image and offers to manage him. Convincing Hancock that he needs to make a change, Ray works on improving the superhero's image, starting with persuading him to serve time in jail for outstanding subpoenas and to do so showing that the city actually needs Hancock. During his incarceration, crime rates rise, which helps Hancock realize the positive impact he can have. Ray also encourages Hancock to be a more responsible and empathetic hero, showing gratitude to the citizens and working within the system. As Hancock begins to take his advice and turn his life around, his relationship with Ray, and by extension with Ray's family, starts to grow, leading to unexpected developments and deeper backgrounds coming to the surface.