Dean Winters (born July 20, 1964) is an American actor, perhaps best known for his portrayal of the Machiavellian Ryan O'Reily on HBO's Oz. He has appeared in the television series Law & Order: Special Victims Unit. He has also made guest appearances on Sex and the City, Third Watch, NYPD Blue, CSI: Miami and 30 Rock as well as previously having a starring role in Rescue Me. He also starred in the 1999 romantic comedy Undercover Angel with Yasmine Bleeth and the 2002 direct-to-video horror sequel Hellraiser: Hellseeker.
Winters was born in New York City, New York, and has three younger siblings, Bradford (a poet/writer), Scott William, and his sister Blair. Scott is also an actor, and portrayed Ryan's own brother Cyril on Oz.Wiki