John Munch is a fictional Detective Sergeant played by actor Richard Belzer. Munch first appeared on Homicide: Life on the Street. Upon that series' cancellation, the character was transplanted to Law & Order: Special Victims Unit, the first spin-off of the Law & Order franchise. He made his 300th appearance on the SVU episode "Unorthodox".
Munch first appears as a central character in the TV series Homicide: Life on the Street, as a homicide detective in the Baltimore Police Department's fictionalized homicide unit, which debuted January 30, 1993. The character was based on Jay Landsman, a central figure in David Simon's true crime book Homicide: A Year on the Killing Streets, a documentary account of the homicide unit's operation over one year. Munch appeared as a regular character in every season, and in almost every episode, of Homicide. Munch's storyline also touched on the relationship between real-life detectives Donald Worden and David Brown, in which Worden was relentless in his tutelage/hazing of the younger detective but also genuinely wanted him to succeed and was impressed when the younger cop did excellent work. A storyline in the book involving Brown cracking a very difficult hit-and-run homicide was included almost verbatim in the show's pilot.
After Homicide: Life on the Street concluded its seventh season in May 1999, the character was transferred into the Law & Order universe as a regular character on Law & Order: Special Victims Unit (both Homicide and the original Law & Order had crossed-over numerous times before, and Munch had featured centrally in each crossover). In the fictional universe, it is explained that Munch had retired from the Baltimore Police Department, took his pension, and moved to New York to join a sex crimes investigation unit, where he was eventually given a promotion to Detective Sergeant.