The season showed how the different gangs fight each other as well as the prison system, culminating in a riot in which the inmates take over Emerald City. Season 1 chronicled the spiritual and political journeys of many of the characters as they descend into insanity, rise and fall politically, and seek redemption.

Williams as Homeboys inmate Kenny Wangler. Recurring guest stars included Adewale Akinnuoye-Agbaje as inmate and Homeboys gang leader Simon Adebisi, Rick Fox as inmate and former basketball star Jackson Vahue, goodfella Mike G as inmate and Schibetta's right-hand man Joey D'Angelo, Stephen Gevedon as biker inmate Scott Ross, Craig muMs Grant as inmate Arnold 'Poet' Jackson, Željko Ivanek as Governor James Devlin, Tim McAdams as Homeboys inmate Johnny Post, George Morfogen as long-term inmate Bob Rebadow, Steve Ryan as corrupt Officer Mike Healy, Lauren Vélez as prison doctor Gloria Nathan, and J. Simmons as inmate and Aryan Brotherhood leader Vernon Schillinger, Lee Tergesen as new inmate Tobias Beecher, Sean Whitesell as cannibalistic inmate Donald Groves, Dean Winters as manipulative Irish inmate Ryan O'Reily, and BD Wong as the prison chaplain Father Ray Mukada. It also stars Kirk Acevedo as Latino inmate Miguel Alvarez, Edie Falco as correctional officer Diane Whittlesey, Rita Moreno as prison counselor Sister Peter Marie Reimondo, Tony Musante as inmate and Mafia boss Nino Schibetta, Leon Robinson as inmate Jefferson Keane, J.K. The first season of Oz stars Ernie Hudson as Warden Leo Glynn, Terry Kinney as Emerald City Unit Manager Tim McManus, Harold Perrineau as inmate and narrator Augustus Hill, and Eamonn Walker as new inmate and devout Muslim Kareem Saïd.

Oz tv series online