Rowena Ravenclaw's Diadem

• Type: Horcrux, Founder's Artefact
• Owners: Rowena Ravenclaw, Helena Ravenclaw, Tom Riddle (Lord Voldemort)
• Maker: Created for Rowena Ravenclaw

The diadem is described as a delicate, tarnished silver tiara of ancient design. It was fashioned to resemble an eagle, the symbol of Ravenclaw House. Etched upon its surface are the famous words of its original owner: “Wit beyond measure is man's greatest treasure.” When Harry Potter first encountered it, unknowingly, in the Room of Requirement, it was sitting atop a warlock's bust, looking simply like a discoloured, old piece of jewellery. However, after it was corrupted by Lord Voldemort's soul, it took on a more sinister quality. When seen with an understanding of its nature as a Horcrux, it seemed to exude a dark power and malevolence.

The diadem's original, intended magical property was to enhance the wisdom of the wearer, a quality that reflected the core values of its owner, Rowena Ravenclaw. Her daughter, Helena Ravenclaw, stole it in the belief it could make her wiser than her famously intelligent mother. After Tom Riddle transformed it into a Horcrux, the diadem became a vessel for a fragment of his soul. This imbued it with powerful Dark Magic, making it extremely resilient and difficult to destroy. Like other Horcruxes, it could only be eliminated by substances or magic of immense destructive power, such as Basilisk venom or Fiendfyre.

The diadem was the most prized possession of Rowena Ravenclaw, one of the four founders of Hogwarts School of Witchcraft and Wizardry. Envying her mother's acclaim and intelligence, her daughter Helena Ravenclaw stole the diadem and fled to a forest in Albania. On her deathbed, a heartbroken Rowena Ravenclaw sent a man who had long loved Helena to bring her back: the man who would later become the Bloody Baron. He found Helena in Albania, but when she refused to return with him, he flew into a rage and murdered her. In his remorse, the Baron then killed himself with the same weapon. Before her death, Helena had hidden the diadem inside a hollow tree. Centuries later, during his time at Hogwarts, Tom Riddle charmed the full story out of Helena's ghost, now the Ravenclaw house ghost known as the Grey Lady. After leaving school, Riddle travelled to Albania, located the hidden diadem, and murdered an Albanian peasant to turn the artefact into his fifth Horcrux. He later returned to Hogwarts under the pretence of applying for the Defence Against the Dark Arts post and hid the diadem in the Room of Requirement, believing its existence and location to be a secret known only to him.

The diadem is first unknowingly encountered by Harry Potter at the end of his sixth year. While hiding his copy of Advanced Potion-Making, he places the diadem on top of a stone bust in the Room of Requirement to mark the location of his book, dismissing it as an “old tiara”. In Harry Potter and the Deathly Hallows, Harry deduces that the lost diadem of Ravenclaw must be one of Voldemort's Horcruxes. After speaking with Luna Lovegood about the diadem and questioning the Grey Lady, he connects the historical object with the tiara he saw in the Room of Requirement. During the Battle of Hogwarts, Harry, Ron Weasley, and Hermione Granger enter the Room of Requirement to find and destroy it. They are ambushed by Draco Malfoy, Vincent Crabbe, and Gregory Goyle. Crabbe unleashes Fiendfyre, a cursed fire he is unable to control. The overpowering Dark Magic of the fire destroys the fragment of Voldemort's soul within the diadem, thus eliminating the Horcrux as the room and its contents are consumed by the inferno.

• Film Adaptation: The destruction of the diadem is portrayed differently in the film Harry Potter and the Deathly Hallows – Part 2. After retrieving the diadem, Hermione Granger gives Harry Potter a Basilisk fang she and Ron Weasley had taken from the Chamber of Secrets. Harry stabs the diadem with the fang, causing a phantom of Voldemort's face to scream out of it. Ron then kicks the destroyed object into the Fiendfyre sweeping through the Room of Requirement (film).