When was the first occurrence of an actor reprising his role as the same character in a totally unrelated show or movie like Bill Nye playing Patterson's father on Blindspot or Ursula Buffay appearing in Friends and Mad About You. Crossovers on the same franchise like Arrowverse and spin-offs are not counted.
Richard Belzer, a former stand-up comedian, played the character of Detective John Munch.
The character of John Munch, as portrayed by Belzer, began in 1993 on NBC's Homicide: Life on the Street, set in Baltimore.
In 1999, Homicide had a crossover with Law & Order. Later in that same year, Munch then joined Law & Order: Special Victims, as a regular character.
In the end, Belzer, as Munch, appeared on NBC's Homicide, Law & Order, Law & Order: SVU, Law & Order: Trial by Jury and 30 Rock. He also appeared (again, as Munch) in Fox's Arrested Development and The X-Files; UPN's The Beat; HBO's The Wire; NetFlix's Unbreakable Kimmy Schmidt; and finally, on ABC's Jimmy Kimmel Live.