Madam Pince in Harry Potter and the Half-Blood Prince

Madam Pince

Madam Pince is the unhelpful librarian at Hogwarts. Of her, J.K. Rowling has said:

"I would like to apologize for you and any other librarians present here today and my get-out clause is always if they'd had a pleasant, helpful librarian, half my plots would be gone. 'Cause the answer invariably is in a book but Hermione has to go and find it. If they'd had a good librarian, that would have been that problem solved. So ... sorry." (source)