There have been several unnamed characters that have appeared on Sesame Street in the role of a Librarian.
In a Cookie Monster sketch, a Large Lavender Live Hand Anything Muppet librarian (performed by Richard Hunt) became extremely frustrated due to Cookie's inability to comprehend that the library doesn't have cookies.
In a "Monster On The Spot" sketch where Telly Monster reports at the library while Debra Starr reports at the airport. When Telly Monster can't hear Debra when the airport gets so loud, he shouts into his microphone to get her to talk louder, but is taken out by the librarian (voiced by Camille Bonora) for loud volume.
Yet another librarian appeared in a sketch with Grover. This Green Anything Muppet Librarian (performed Jerry Nelson) kept telling Grover, who was trying to explain what goes on in a library, to talk more and more quietly until he could not be heard at all.
Other librarians in the Sesame Street universe include Linda, Lisa, Mrs. Turow, Dalia, and Jesse. While not officially librarians, Maria worked as a part-time assistant at the Sesame Street Library when she was still in school; and Grover would often assist her at the library.