Recurring
George Gore II as Gregory "G" Williams: Gregory is the son of J.C. Williams and Chantel Tierney. In the pilot episode, he is described as a nine-year-old. For most of Season 1, his given age is 10. By the beginning of Season 3, his given age is 13 and by season 4, his given age is 14. He is the only recurring character to appear in all four seasons.
Michael Michele as Sandra Gill (season 1): Sandy is an attorney in her late twenties. Throughout Season 1, she was involved with J.C. Williams. She became pregnant with J.C.'s baby and agreed to marry him, but was murdered on the eve of their wedding by Danny Cort, a criminal with a vendetta against J.C.
Fatima Faloye as Chantel Tierney (seasons 1–3): Chantel is a registered nurse in her late twenties. She has a son, Gregory, to whom she gave birth as a teenager with then-boyfriend J.C. Williams.
Kamar de los Reyes as Luis (season 2): Luis was the teenage boyfriend of Nina Moreno, whom he married after she became pregnant. The child, a girl, was placed for adoption and given the name Melissa Lewis. Luis soon abandoned Nina. While she moved on with her life, Nina never divorced Luis. Years later, after he and Nina finally agreed to begin divorce proceedings, Luis was killed during a mugging.
Roger Robinson as Major Harold Williams (season 3): An officer with the United States Army Special Forces, he is the father of J.C. Williams. He abandoned his wife and son, and did not contact J.C. again for 17 years.
José Perez as Mike Torres (seasons 1–3): Mike is a jazz and salsa musician, and a recovering heroin addict. Having alienated much of his family over the years, he is closest to his son Eddie.
José Zúñiga as Father Jimmy Torres (seasons 1–2): Jimmy is a Catholic priest, and the older brother of Eddie Torres.
Lisa Vidal as Carmen Torres (seasons 1–2): Carmen is a newspaper reporter, and the sister of Eddie Torres.
Nancy Ticotin as Teresa Torres Rivera (seasons 1 and 3): Teresa is the well-to-do sister of Eddie Torres.
Steve Ryan as Dave Cooper (seasons 2–3): Dave is the husband of Virginia Cooper.
Eden Riegel as Megan Cooper (seasons 2–3): Megan is the daughter of Virginia Cooper. As a preteen, Megan befriends a man in an online chat room. When she meets him in person, he kidnaps and rapes her. During his subsequent attempt to avoid arrest, the man is shot and killed by Virginia.
Marina Durell as Sgt. Sonia Moreno (seasons 2–3): A sergeant with the NYPD, she is the mother of Nina Moreno.
Zoe Dora Lukov as Melissa Lewis (season 3): Melissa is the biological daughter of Nina Moreno and her first husband Luis. Because her parents were still teenagers when she was born, she was placed for adoption.
Dean Winters as Paul Delany (season 4): A firefighter with the FDNY, he is the brother of Nell Delany.
Jennifer Esposito as Gina D'Amico (season 4): The former lover of Alec Stone, she is now married to his brother Frankie D'Amico.
Justin Theroux as Frankie D'Amico (season 4): An organized crime boss with the Brooklyn-based D'Amico Family, he is the brother of Alec Stone.
Sean Squire as Roger (season 4): Roger is the maternal half-brother of Malcolm Barker. He and Malcolm are estranged.
Novella Nelson as Malcolm Barker's Mother (season 4)
Frank Pellegrino as Det. Ricciarelli (seasons 1–2)
Jim Moody as Det. Otis "Old School" Washington (season 1)
Gilbert Lewis as Det. Otis "Old School" Washington (pilot episode only)
Takeo Matsushita as Medical Examiner Wong (season 1 episodes 3, 4 & 5)
Lee Wong as Medical Examiner Wong (seasons 1–3)
James Saito as Det. Chang (season 1)
Jon M. McDonnell as Detective Sweitek (seasons 1–2)
Michelle Hurd as A.D.A. Maria Reynolds (seasons 1–2)
Edie Falco as Sgt. Kelly (seasons 2–3)
James McCaffrey as Capt. Arthur O'Byrne (season 3)
Joe Lisi as Chief of Detectives (season 4)
John Costelloe as John Santucci (seasons 1–3): Santucci is an organized crime boss connected to the Gambino Family. He was a childhood acquaintance of Eddie Torres, and there is personal animus between the two.
Ice-T as Danny "Danny-Up" Cort (seasons 1–2): A chemistry wiz, Cort was a rising drug kingpin until being apprehended by detectives from the Fourth Precinct. After J.C. Williams killed his brother in a police shootout, Cort retaliated by murdering J.C.'s pregnant fiancée Sandy Gill, igniting a bitter feud between the two men, which only ended after J.C. killed him in self-defense.
Giancarlo Esposito as Adolfo Guzman (season 2): Guzman was a childhood rival of Eddie Torres, and as an adult became a criminal associate of John Santucci. The animus between Eddie and Guzman grew when Guzman attempted to take over Mike Torres' nightclub.
Naomi Campbell as Simone Jeffers (season 2): Sometime after Sandy Gill's death, Jeffers seduced J.C. Williams as part of a revenge plot instigated by Danny Cort.
Ernest Abuba as Sonny Fung (season 3): Fung was an organized crime lord in the Chinatown section in Manhattan. He ordered the death of Tommy McNamara's father, a corrupt police officer secretly working with Fung. Years later, Fung is killed in a shootout by another corrupt police officer, Harry Bennett (the elder McNamara's former partner).
Dana Eskelson as Nadine Jordan (seasons 3–4): Jordan was part of a highly skilled bank robbery team, and was responsible for the murder of Detective Tommy McNamara after discovering he was a cop that had infiltrated her crew. Eventually, every member of her crew was captured or killed by the police, with her husband being amongst the fatalities, but she escaped. In retaliation for her husband's death, she killed Eddie Torres, becoming the primary enemy of J.C. Williams (Eddie's best friend) and Nina Moreno (Eddie's bride and Tommy's partner) during the fourth and final season. Nadine is eventually captured and convicted of her numerous crimes (including Eddie and Tommy's murders), but is spared the death penalty and given life without parole, much to J.C. and Nina's dismay. Nina eventually kills her in self-defense during an undercover operation in a prison.
Victor Colicchio as "Slick Rick" (season 1): One of Eddie Torres' confidential informants.
Elizabeth Rodriguez as Gina (season 1): Eddie Torres' off-and-on girlfriend during Season 1.
Gladys Knight as Natalie (season 1): The original owner of Natalie's, the nightclub which appears in virtually every episode of the series' first three seasons.
Rosanna Scotto as Herself (seasons 1–3): She is a television reporter for WNYW, the Fox station in New York.
Isaiah Washington as Andre Morgan (season 2): An ex-convict released on parole, Andre is a single father whose son is a friend and hockey teammate of J.C. Williams' son Gregory.
N'Bushe Wright as Carol (season 2): Carol is Andre Morgan's parole officer. She dates J.C. Williams briefly.
Tyra Banks as Natasha Claybourne (season 3): Natasha is Gregory Williams' French teacher. She briefly dates J.C.
