He is portrayed by Daniel Craig.
Connor is the mentally unstable and violent son of an Irish mob boss named John Rooney, who is jealous of his father's relationship with Michael Sullivan, Rooney's enforcer and foster son. He frequently acts out against his father by needlessly killing people the elder Rooney simply wants "straightened out", and is secretly embezzling from the Rooney "family business". he is the thorn in his father's side and is widely disliked throughout his father's organization; Frank Nitti, Al Capone's right-hand man and Rooney's erstwhile business associate, calls Connor "a big baby who doesn't know his thumb from his dick".
During a meeting between Connor, Sullivan and one of Rooney's associates, Finn McGovern, Connor murders McGovern in cold blood, an act which is secretly witnessed by Sullivan's son Michael. Sullivan swears his son to secrecy while Rooney tries to force Connor to apologize for what he has done. Humiliated, Connor gets back at Sullivan by ordering his men to kill Sullivan's wife and younger son Peter (mistaking him for Michael). Sullivan, wanting revenge, goes to Capone to seek work and also to discover the whereabouts of Connor, who has gone into hiding. Instead, Rooney is informed of the meeting and, fearing for Connor's safety, reluctantly allows Capone to send assassin Harlen Maguire to kill Sullivan.
Sullivan escapes from Maguire and eventually ends up being forced to kill Rooney, who claims he is glad that Sullivan is his killer. No longer seeing a reason to protect Connor, Capone reveals to Sullivan the hotel he is staying at. Sullivan immediately travels there and shoots Connor in the head as he is taking a bath.