There wasn't one librarian throughout history. As long as someone appeared with more potential than the previous librarian, the tower would lure it through Solution, which was why there were two sides to the gate. Solution to pull to the tower and Answer to receive the individual, they would apply the opposite if someone wanted to go out. The tower accepted anyone seeking knowledge but it would take something in exchange for that knowledge one desired. The price varied from one to another and from the level of knowledge sought to another.
Answer was a succubus before; she became a librarian because the previous one tricked her. It was a male one. She didn't remember much of that time since a long time passed; she even forgot her own name. Librarians all forgot it since everything and everyone inside the tower never called her by her real name. That was the real face of the tower. Its core magic functioned at the price of sacrifices.
