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).

Even though Brian Cassidy is a dedicated member of the Special Victims Unit, he lacks the language to describe sex crimes and the emotional maturity to deal with them.

Cassidy has a drunken one-night stand with fellow SVU Detective Olivia Benson (Mariska Hargitay) but wants to pursue a relationship with her.

After she details how her abuser systematically violated her and then had her gang-raped, Cassidy decides he lacks the stomach to deal with sex crimes and transfers to the NYPD's Narcotics Division.

Because of the longtime consensual relationship Cassidy had had with a prostitute during his undercover stint, however, he is demoted from detective to officer, working nights at a Bronx courthouse.

Although the assignment very nearly leads to his death at the hands of two corrupt cops, it is revealed in the episode "Rapist Anonymous" that Cassidy is a detective again and will be working in Internal Affairs.

Cassidy and Benson amicably break up during the episode "Downloaded Child" after realizing they are fundamentally different people; he prefers to live in the moment, while she plans for the future.

In "Mood", it is revealed that Cassidy told another DA investigator about Benson and her ordeal with serial rapist William Lewis (Pablo Schreiber), which indirectly led to the child abuse claim.

However, Cassidy opens up to Stone, telling him that he was molested as a child by his Little League coach, something he never told Benson, and that one reason he left the unit was his inability to handle the recurring memories of his abuse.

Although Winters previously worked with Dick Wolf on New York Undercover,[9] he credited fellow cast member Richard Belzer with getting him the job on Law & Order: Special Victims Unit.

During the 13th season, SVU was filming scenes in front of the building where Winters lived, so he chatted with the cast and crew, especially his former costar Mariska Hargitay.

Winters saw potential in the storyline involving Cragen being framed for the murder of a prostitute and believed the time was right, so he agreed to stay on as a recurring character in the 14th season.