Wiseguy
Wiseguy (1987-1990) was a television show about an OCB (Organized Crime Bureau) undercover agent named Vincent "Vinnie" Terranova played by Ken Wahl. It was produced by Stephen J. Cannell.
There were two substitute agents: John Henry Raglin (played by Anthony Denison) took over from Vinnie for the "Rag Trade" story arc. The last few episodes of the series had Vinnie substituted by Michael Santana (played by Steven Bauer). The regular cast also included "Lifeguard" a.k.a. Daniel Benjamin Burroughs played by Jim Byrnes and Frank McPike played by Jonathan Banks.
A follow-up movie (starring Vinnie) was made in 1996.