Season 1 In the pilot episode, O’Reily bribes guards in solitary confinement to allow Johnny Post to set
Dino Ortolani on fire, before betraying Post to the Italians. Later in the season, he attempts to orchestrate
Jefferson Keane’s death. This plan, however, fails as Keane kills one of his attackers. O’Reily then partners with
Simon Adebisi to murder
Nino Schibetta. The two feed him ground glass for several weeks, haemorrhage internally. Upon his death, O’Reily consolidates influence in the prison drug trade. He also supplies Tobias Beecher with heroin, contributing to his addiction and subsequent PCP-induced violent breakdown, during which he blinds
Vernon Schillinger in one eye.
Season 2 O’Reily is diagnosed with breast cancer and undergoes chemotherapy under
Dr. Gloria Nathan. He develops romantic feelings for her and arranges for his brother to kill her husband. Cyril is subsequently imprisoned in Oz, where he is sexually assaulted by Schillinger and the
Aryan Brotherhood. In exchange for his brother's release, Ryan eventually confesses to orchestrating Preston Nathan’s murder, leading to his own indictment.
Season 3 O’Reily allies with Beecher and
Chris Keller against Schillinger. When Schillinger’s son Andrew arrives in Oz, he pressures him into buying drugs, and later tortures him for refusing. After Andrew publicly humiliates his father and the Aryan Brotherhood by renouncing beliefs on racial supremacy, Schillinger gives him heroin, resulting in his overdose and death. O’Reily also develops a friendship with the new CO supervisor,
Sean Murphy. During Murphy’s inmate boxing tournament, O’Reily ensures Cyril’s victory by drugging his opponents,
James Robson, Miguel Alvarez,
Chucky Pancamo, and
Hamid Khan, with
chloral hydrate. He then orchestrates the death of
William Cudney, who threatened to expose his actions. At the end of the season, Oz is forced into lockdown because of racial unrest due to Cyril's defeat of Khan.
Season 4 O’Reily and Cyril participate in restorative justice sessions with Dr. Nathan and her late husband’s parents. She is later assaulted by Patrick Keenan and suspects O’Reily arranged it. He falsely claims responsibility and later kills Keenan. O’Reily also manipulates events leading to the dismissal of Unit Manager Martin Querns, restoring Tim McManus as unit manager. He also has a dispute with Nikolai Stanislofsky over a contraband cell phone, leading to the latter’s death at the hands of Officer Claire Howell, with whom O’Reily has a brief sexual relationship. Later,
Martin Querns replaces McManus as unit manager and shifts control of Em City toward Adebisi’s allies. O’Reily and Keller retaliate by murdering
Nate Shemin and
Mondo Browne and framing Supreme Allah, which results in Querns’s dismissal and McManus’s reinstatement. In the second half of the season, a television crew comes to film at Oz under journalist Jack Eldridge, who had earlier exposed the O’Reilys’ crimes. Ryan refuses to cooperate with the filming as retribution. Supreme Allah, released from solitary confinement, threatens O’Reily, who then arranges to have him killed by
Tug Daniels. Around this time, Suzanne Fitzgerald visits, claiming to be O’Reily’s mother. Despite his initial disbelief, he eventually accepts her after confirmation from his father.
Season 5 Jia Kenmin conspires with
Li Chen to target the O’Reilys, leading Cyril to fatally stab Chen during an altercation. Cyril is tried for murder, with his family declining to intervene due to his mental state. Meanwhile, O’Reily shares a cell with
Father Daniel Meehan, who counsels him during Cyril’s trial. Upon discovering that Glen Shupe had been bribed to lie, O’Reily orchestrates retaliation with the Latinos, ultimately resulting in Shupe’s mutilation and Jia’s death at the hands of guards. He then, with Meehan's guidance, begins confronting his childhood trauma and supports Cyril’s appeal.
Season 6 O’Reily pressures Shupe to confess, but the testimony fails to aid Cyril’s defense. Meehan dies of a brain embolism, and O’Reily washes his body in the morgue while reading a passage out of the bible. Rumors then spread that Peter Schibetta cursed O’Reily. He, however, manipulates Chucky Pancamo into believing Schibetta threatened him as well, leading the Italians to murder Schibetta. Cyril’s execution is briefly stayed after inmate
Jahfree Neema organizes a protest. Despite this, however, Cyril is eventually executed, leaving Ryan devastated. He subsequently begins a romantic relationship with Dr. Nathan. Later, O’Reily reconciles with his father, Seamus, who expresses remorse after years of neglect. He is last seen accompanying Seamus onto a bus during an attack on Oz. ==Reception==