Eleanor Twitty
Eleanor Twitty was a ghost who haunted the New York Public Library. Once an ordinary librarian, Twitty was murdered by rare book collector Edmund Hoover after she refused to give him the Gozerian Codex. Her ghost haunted the New York Public Library for several years. She was known as "The Gray Lady." Ordinarily benign, she could become easily enraged, transforming into a hideous monster and lashing out at those who earned her ire.
After she terrorized librarian Alice Melvin, library administrator Roger Delacourte called Dr. Ray Stantz at Columbia University. Stantz, along with his colleagues Dr. Egon Spengler and Dr. Peter Venkman, arrived later that day to investigate, but were driven away by Twitty's ghost.
Later, after the group had officially become the Ghostbusters, they returned to the library to defeat the Gray Lady once and for all. Stantz, Spengler, Winston Zeddemore and a rookie Ghostbuster fought their way through Twitty's armies of book golems, as well as two particularly ferocious ghosts named Cruster and Crusto, before they finally defeated Twitty in the libray's sub-basement.