Was a middle class lawyer in denial about his alcoholism until landing in prison forced him to confront himself and become self-sufficient. His character undergoes the most drastic changes throughout the seasons, during which he becomes a drug addict and falls in love with a man. His relationship with Keller and blood feud with Schillinger is the series' dominant story arc, beginning in the first episode and being resolved during the series finale, when he accidentally kills Schillinger in an acted fight in a play
Leader of the Aryan Brotherhood, Schillinger commits atrocities against other inmates because of race, sexual orientation, or overall weakness. However, he is double-crossed by Keller and accidentally killed by Beecher during a production of the play "Macbeth"
An elderly inmate serving life for murder. He was originally sentenced to death, but in 1965, he survived a botched execution and had his sentence commuted. He is fantastically intuitive (some think as a result of the botched execution), which in the first couple of seasons he explains by nonchalantly saying "God told me"; later he begins doubting the source and veracity of his insights.
A brilliant Muslim leader with a powerful voice and a conviction that other people's racism will absolve him. He is responsible for the death of Simon Adebisi; however, it was ruled self-defense. He is shot and killed by Lemuel Idzik, played by Joel Grey.
Undergoes a process of losing masculine credibility within the Latino gang, then tries to redeem himself after cutting out a respectable prison guard's eyes. He briefly escapes from prison, but is eventually recaptured.
Ryan O'Reily's mentally handicapped-brother, who was incarcerated after blindly following Ryan's orders to murder the husband of Dr. Gloria Nathan, with whom Ryan is obsessed. He was mentally incapacitated in a gang fight. He kills an inmate out of self-defense of his brother, but gets sent to death row and is finally executed, after a long legal battle.
A bisexual serial killer who preyed upon gay men in the outside world while hiding his sexual orientation through a series of marriages. Perhaps the most amoral figure in the entire milieu, he is a master of emotional manipulation and only seems to really enjoy himself when those who care about him are made to suffer. His relationship with Beecher is also a big part of many episodes. He's killed by Tobias Beecher in the show's finale episode, who considers Keller guilty of sending him back to Oz.
A gigantic, deranged maniac of Nigerian descent; incarcerated for decapitating a police officer with a machete. His flirtations with insanity and religion are transient. However, Adebisi remains one of the most powerful inmates within the walls of Oz, until his death when he is killed by Kareem Said.
The corrections officer (COs) are mostly white (predominantly Irish and Italian) with many black and some Latino officers. The warden, Leo Glynn is African American and started off his career as a CO at Oz. Most of the COs come from lower socio-economic classes. Some are amoral and prone to corruption. The main unit manager, Tim McManus, is the only authority figure who has not started off as a guard and this therefore gives him a different point of view about how to deal with the inmates. The rest of the non-correctional staff, such as Dr. Gloria Nathan and psychiatrist Sister Peter Marie ("Sister Pete") Reimondo, have a much more humane view of prisoners, and often push Glynn and the others to see the inmates as human beings. Overall, different factions within the staff are almost always at odds, trying to manage internal problems while keeping the public calm regarding the way the prison is being managed.
Warden Leo Glynn played by Ernie Hudson. A conflicted person trying to maintain law and order in an often chaotic environment. He does what he can to manage every conflict present in Oz. Sister Pete calls him "the best man for the worst job." Appears in episodes 1–55.
Tim McManus played by Terry Kinney. A liberal idealist who forms Emerald City for purposes of making a perfect prison where rehabilitation and conflict are resolved. Often seen as weak for supposedly soft approaches to dealing with the inmates, he still manages to come out on top of many situations. Appears in episodes 1–26, 28–56.
Diane Whittlesey played by Edie Falco. A CO, raised in poor conditions and uneducated, who is faced with managing several issues at home, a relationship with McManus, and being fair to the inmates. Appears in episodes 1–18, 20–24.
Dr. Gloria Nathan played by Lauren Velez. A prison doctor who leads the prison hospital in providing care for several of the inmates within Oz. A good person, she deals with conflict all the time, whether it is from the inmates such as Ryan O'Reily, or state medical boards. She manages to come out calmly throughout any conflict.
Claire Howell played by Kristin Rohde. A female CO, she is extremely unstable and prone to sadistic sexual violence. She has sexual relationships with several staff members and inmates in order to dominate them. She eventually begins to change after learning that she is pregnant, probably by Carlos Martinez. Appears in episodes 17–39, 41–56.
Sean Murphy played by Robert Clohessy. An Irish CO, Murphy is the staff member most trusted by McManus. A fair and confident officer, Murphy maintains order to the best of his ability in Oz while doing what he can to support McManus' ideology. He is more honest and competent than the other guards and Warden Glynn also holds him in high regard. Appears in episodes 18–55.
Clayton Hughes played by Seth Gilliam. A young and conflicted African American officer, Hughes is very close to Glynn. Hughes' father was Glynn's best friend and was killed while working as a CO when Hughes was seven years old. After being convinced by Adebisi that his father's murder was racially motivated, Hughes becomes a Black Militant and attempts to murder the governor. Hughes is sent to Unit-J in Oz which is meant for ex-cops and ex-correctional officers. In Unit-J he kills Desmond Mobay aka John Basil. Then he is sent to Solitary, where he gets "accidentally" killed when attempting to assassinate Leo Glynn.
Karl Metzger played by Bill Fagerbakke. A white supremacist guard who took over Whittlesey's position in Emerald City after she was transferred to General Population. He is secretly a member of the Aryan Brotherhood, and once did a favor for two Aryans by forcing Busmalis and Rebadow to give up their cell, which contained a tunnel. Tim McManus found out that he has connections with the Aryans, but could not do anything about it before Metzger was killed by Beecher.
Martin Querns played by Reg E. Cathey. A jaded and results-oriented black man, Querns is hired by Glynn after pressure by community leaders and the black prison population, led by Adebisi, to hire an black Unit Manager to replace McManus. Querns, as told through a conversation to Adebisi, is only different from the black inmates in that he has been smart enough to have never been arrested for dealing drugs. The complete opposite of McManus, he believes that drugs are good for the prisoners because they subdue them until they are incapable of any discipline problems. He runs Emerald City by making Adebisi and his partners in Oz's drug trade the main trustees, allowing them to do all the drugs that they wish as long as no violence occurs in Emerald City. Kareem Said and McManus completely oppose this which leads to his firing. His efficiency, however, gets him promoted to the position of warden at another state correctional facility and he transfers back to Oz following the death of Leo Glynn.
Officer Mike Healy (Steve Ryan) A disgruntled and corrupt officer, Healy has a very low opinion of both the inmates and Unit Manager Tim McManus. Healy is friends with inmate Ryan O'Reily and is a friend of Ryan's brother. Healy and O'Reily run a drug operation in Oz. When Mafia boss Nino Schibetta sees that Healy is competing with him in selling drugs, he makes a deal with O'Reilly. O'Reilly is told he will be a permanent ally of the Italians if he shuts down Healy's operation. Knowing the politics of Oz, O'Reilly gets inmate Ronald Pokelwaldt to alert the COs of a drug deal going on between Healy and O'Reilly where the two are immediately arrested. When Healy is fired and charged, O'Reilly refuses to testify spending a month in the hole, but makes sure his scheme shall never be discovered by ratting Pokelwaldt to the hacks, who hospitalize him. He recovers fully and quickly, however, as he attends a drug-counseling session shortly after his beating with no signs whatsoever of any trauma.
Stella Coffo (Patti LuPone). The librarian of Oz. Adored by Robert Rebadow (who works with her in the library), she is reserved in returning his affection because of his reaction to her breast cancer diagnosis.
Suzanne Fitzgerald (Betty Buckley): Inmate Ryan O'Reily's biological mother. Musical arts teacher at Oz.
Governor James Devlin played by Zeljko Ivanek. A right-wing politician, Governor Devlin represents all extreme mechanisms of law and order necessary to keep society crime free. He passes several acts to minimize prisoner rights and increase law enforcement spending. Disliked by several staff members and the vast majority of the inmates, Devlin eventually is in a sea of controversy once a city mayor whom he was politically involved with is sent to Oz for conspiring to commit a racially motivated bombing.
Alvah Case played by Charles S. Dutton. Law school Dean; he investigates the prison riot after season one and, in season four, runs for governor against Devlin.
Pierce Taylor played by Robert John Burke. Another FBI agent who often visits Oz (starting in the fourth season) to investigate murder cases. Generally very effective at his job, but insensitive to the needs of inmates. He essentially replaces Jeremy Goldstein
Miss Sally's Schoolyard (Miss Sally played by Whitney Allen) is a puppet show that the inmates enjoy watching because Miss Sally has large breasts.
Due to Emerald City's unconventional configuration and routine, each new inmate is given a sponsor to help acclimate. Inmates are generally paired with sponsors of similar nationality, background, race, and/or religion, to help acclimate, with the help of someone with similar interests and beliefs. Specific requests for current Emerald City prisoners to be paired up with inbound inmates have occasionally been made and granted. Below is a list of inmates and sponsors.