Special Delivery Kluger is the narrator of the Rankin/Bass Christmas television special Santa Claus is Comin' to Town. S.D. is a friendly mailman who drives a snowmobile/mail truck, and tells the local children how Santa Claus came to be when his truck breaks down. He recites the entire story of Santa Claus's origins, including how he met his wife Jessica, how he got his magic powers from the Winter Warlock, how elves came to be, and showing the origin of the flying reindeer. When he finishes his story, his truck has been mended, and he resumes making his mail delivery to Santa and Jessica, singing the titular song.
S.D. later reappeared as the narrator in another Rankin/Bass holiday special - The Easter Bunny is Comin' to Town, in which he answered questions about the origins of the Easter Bunny. In that special, it was notably revealed that, as a kid, S.D. was a citizen of Kidville and also drives a steam train to deliver letters and Easter goodies to help the Easter Bunny.
The character is a caricature of his performer, Fred Astaire.