The Smurfs were created by the Belgian artist Peyo in 1958 and later starred in a successful Hanna-Barbera animated series.
Some of the Smurfs, including Papa Smurf and Brainy, appeared with the Muppet Babies in the 1990 animated television special Cartoon All-Stars to the Rescue.
References
In Muppets Tonight episode 205, Don Rickles is hired by Ernst Stavros Grouper to act as therapist and boost the morale of the Muppets. Rickles reports, "I talked to your happy little Smurf friends."