Each week, viewers saw the gritty reality of life in a New York City Police unit, as the officers go about their work with a grim determination, and a willingness to break the same laws that they're supposed to be enforcing. Two partners, Detectives Andy Sipowicz (Dennis Franz) and John Kelly (David Caruso) (later replaced by Bobby Simone (Jimmy Smits)), were the central characters in this weekly Police drama, and personified very different approaches to their difficult job. Sipowicz's brash gruffness (covering an emotional vulnerability) was tempered by the precise and controlled demeanor of the two partners with whom he has worked.