Detective Brian Cassidy is a fictional character played by Dean Winters in the American crime drama television series Law & Order: Special Victims Unit on NBC. A recurring cast member during the first season, Cassidy is a young and inexperienced detective with the New York Police Department's Special Victims Unit, and the original partner of John Munch (Richard Belzer). The stress of the Special Victims Unit is too much for Cassidy, and he transfers to the Narcotics unit in the middle of the season. Cassidy later returns in the 13th-season finale working undercover for a pimp the SVU detectives are investigating. Winters had previously worked with creator Dick Wolf, but he was offered a role on SVU through Belzer, though the role proved to be temporary due to Winters' commitment to Oz. As