Character from harry-potter-deathly-hallows by
Helena Ravenclaw, ghost of Ravenclaw Tower -- she told Tom Riddle where to find her mother's diadem and has carried the shame ever since. She tells Harry the truth because she recognizes he is different.
Helena stole her mother Rowena Ravenclaw's diadem to make herself cleverer and fled to Albania. The Bloody Baron found her and killed her when she refused to return. She kept the diadem's location secret for a thousand years until a charming young student named Tom Riddle convinced her to reveal it -- using the same manipulative sympathy that worked on everyone. She has never forgiven herself for being fooled. When Harry finds her during the Battle of Hogwarts and asks about the diadem, Helena resists. She recognizes the pattern -- another urgent young man, another request for her mother's legacy. But Harry is honest where Riddle was calculating. He tells her the truth about what Riddle did with the diadem. She tells him it's hidden in the Room of Requirement. Her shame becomes the key to destroying a Horcrux.
Tall, beautiful, translucent ghost with waist-length hair. Proud bearing, sorrowful expression. Medieval gown, floating silently through the castle.
Also known as: Helena Ravenclaw, The Grey Lady, Helena