A librarian is someone who works in a library maintaining books and information and lending them to patrons. If you have a research project ahead of you, make friends with the librarian.
There are many different types of librarians, from archivists who care for, organize, and lend very old or valuable documents; to school librarians who organize book-related projects and buy books and electronic resources that are appropriate for the students they serve. To become a librarian, you might want to get an advanced degree in library science. The Latin root of librarian is liber, "book." In the 17th century, a librarian was known as a "library-keeper."