The lost diadem of Ravenclaw was a sapphire-encrusted tiara once belonging to Rowena Ravenclaw and etched with the Hogwarts founder's famous quote: "Wit beyond measure is man's greatest treasure." The diadem was said to increase the wearer's wisdom, to the extent it made Rowena's daughter, Helena Ravenclaw, deeply jealous. When Helena stole the diadem and ran away from home, a distraught Rowena sent The Bloody Baron to find her. Tragically, this event ended in Helena's murder. Thought to be lost for centuries. eventually, Tom Riddle discovered its whereabouts, transforming it into a Horcrux. But this wasn't the end of the diadem's story.