Masterpiece Theater is a long-running PBS anthology series, originally hosted by Alistair Cooke. The series was regularly spoofed on Sesame Street as "Monsterpiece Theater". The latter actually changed its opening titles to reflect changes to the original Masterpiece.
Though most of the "Monsterpiece" sketches ranged from classic literature to popular films and plays or even television shows, some of the earliest sketches spoofed actual Masterpiece Theater series, such as Upstairs, Downstairs and I, Claudius.
Masterpiece Theater was among the PBS shows mentioned by Kermit the Frog in Sesame Street, Special when trying to find reasons for Oscar the Grouch to like public television. Telly Monster also mentions it in a list of shows beginning with M in a 1979 episode.