Junior is a dad's boy. His father is a Senator and his uncle is a Cardinal. They pretty much rule the city. Junior has a thing for very young girls. He only gets a turn on when they scream. He firstly rapes then kills them. John Hartigan got into his way and managed to save a little girl named Nancy. John shot him a couple of times; one of the shots was aimed at his penis. Junior didn't die that night but he lost a lot of blood. His father paid a lot of money to a lot of doctors to restore his penis. The medicines used affected Junior's skin. It turned yellow and his body had a strange smell. While Hartigan was in prison, something that Senator Roark set up, Junior was able to enjoy his perversion. He took revenge on Hartigan by visiting him in prison convincing him that he had found Nancy and had hurt her. Hartigan fell for Junior's ruse, escaped prison and tried to find Nancy. When he discovered that Nancy was alright, he realised that he had been tricked.
Junior followed them and kidnapped Nancy. Even the fact that she was too old for his taste (Nancy was 20 at that point), he tortured her and try to rape her again. Nancy didn't scream so Junior was getting angrier by the minute.
Hartigan managed to get there in time and beat Junior to death, saving Nancy for a second time.
Sin City Movie
Roark Junior was portrayed by Nick Stahl in the Sin City movie adaptation.