So I was watching an episode of Barney Miller and I spotted Ron Carey in a bit part as a jewel burglar. As most of you know, Carey later became a series regular as Officer Leavitt. Dennis Franz first appeared on Hill Street Blues as a crooked cop before assuming the role of Detective Buntz. It made me think there are likely any number of actors with similar histories. Any come to mind?
The IMDB tells me Bernie Kopell appeared as Siegfried in 14 episodes of Get Smart. There were 138 episodes, so that's roughly one in ten.
King Moody played Starker in 7 of those episodes, for the first time in season 2. He had previously appeared in two other roles, and he had yet another before his second appearance as Starker.