Richard Belzer was once called a "lousy actor," but his character Detective Munch has appeared on more TV shows than any other!

When Richard Belzer first auditioned for the role of Detective John Munch on NBC's Homicide: Life on the Street, executive producer Barry Levinson called him a "lousy actor," urging him to practice his lines and audition again. Though Belzer was reportedly "still terrible," he landed the role that would see him portray the cynical detective on ten different shows over the course of twenty years.

After numerous crossovers between Homicide: Life on the Street and Law & Order: Special Victims Unit, Munch officially became part of the New York squad after Homicide aired it's final episode in 1999.

With additional guest appearances, including The X-Files, Arrested Development, 30 Rock and The Wire, Munch is the only fictional character to be portrayed by the same actor spanning 10 TV shows on 5 different networks. An appearance on Sesame Street as his very own muppet showed Munch solving alphabet-related crimes.

Detective John Munch was originally based on the David Simon true-crime book, Homicide: A Year on the Killing Streets, which documented the Baltimore Sun writer's year with the Baltimore Police Department's Homicide Unit. Fictionalized for TV, the character of Munch was based on real-life homicide detective Jay Landsman.

After twenty years in the force, Detective Munch retired on the October 16, 2013 episode of Law & Order. As TV history shows, we may not have seen the last of him.

(Source)