S. Morgenstern (the "S" stands for Simon) is author William Goldman's whimsical narrator of The Princess Bride and The Silent Gondoliers.
Morgenstern's is a sweetly cantankerous authorial voice, prone to all manner of entertaining tangents.
According to his fictional biography in the books, he lives in Florin City where he dotes on his wife, two daughters, and four-and-a-half grandchildren. He supposedly lived in Venice to complete his research for The Silent Gondoliers, and his love of baseball makes it obvious he's spent time in the United States.
However, English is not his native language; in a letter to the editors at Del Rey, he wrote of Gondoliers "although I have written in French and German as well as Florinese, this is my first attempt at colloquial English."
Furthermore, Morgenstern is evidently quite old, possibly older than his creator Goldman (who is 71). Further on in the Del Rey letter, he requests that the editors fix some inaccuracies for the next edition of The Princess Bride:
"You say in several places that I am dead. As I sit here and watch my fingers form this note, I am forced to believe that you are in error. I am old, but alive. Perhaps as you age, you will find the two are not mutually exclusive."
Perhaps this is an indication that someday we may see another Goldman novel come out under S. Morgenstern's pseudonym. And that would be very, very cool.