Jocasta Nu is a human Jedi Master from Coruscant and Chief Librarian of the Jedi Archives, introduced in Attack of the Clones (2002) and played by Alethea McGrath. She appears for one scene, helping Obi-Wan Kenobi look for a planet that is not in the records.
That scene is one of the most quoted in the prequels for a reason. Told that Kamino is missing from the Archives, she replies that if an item does not appear in the records, it does not exist — and she is wrong, and the Order dies partly of that certainty. StarWars.com's databank puts it in almost the same words: she can be too confident that the Archives hold the right answer to every question.
Later material has been kind to her. Marvel's canon comics give her a post-Order 66 afterlife in which she goes back into the ruined Temple for the Jedi holocron list — the names of every Force-sensitive child in the galaxy — precisely so the Empire cannot have it. The librarian turns out to be the one who understood what the Archives were actually for.
She is also, structurally, the Order's memory. Every argument this site's Fall of the Jedi pages make about institutional blindness runs through her desk.