This article is from the Libraries FAQ, by Anthony Wilson firstname.lastname@example.org with numerous contributions by others.
The following comes from Grimes, Deborah J. "Marion the Librarian -
The Truth Behind the Image" in Scherdin, Mary Jane (ed.) _Discovering
Librarians: Profiles of a Profession_ (Chicago: ACRL, 1994), pg. 3:
"In 1950, Meredith Wilson wrote a musical entitled _The Music Man, in
which the lead female character is Marian Paroo, a small town
librarian and music teacher. The character is a self-proclaimed
spinster, who must continually resist the exhortations of everyone
around her, including the mother with whom she lives, to "find a man".
Marian is characterized as picky, hardworking, standoffish, bookish,
and, by most accounts, pitiable. The phrase, "Marian the Librarian",
was coined, along with the image, in a song in The Music Man. Over
forty years later, the image continues to permeate public opinion and
remain the stereotype of the professional librarian."