Helena Ravenclaw, more commonly known as “The Grey Lady”, is the ghost of Ravenclaw house and the daughter of Hogwarts founder Rowena Ravenclaw. She told Lord Voldemort (and later, Harry Potter) about the lost Ravenclaw diadem which she stole from her mother and hid in Albania. Helena was killed by the Bloody Baron when she refused to return with him to see her fatally-ill mother.