The Diadem of Ravenclaw

• Type: Horcrux, Magical Artefact
• Owners: Rowena Ravenclaw, Helena Ravenclaw, Tom Riddle (Lord Voldemort), Harry Potter (briefly)
• Maker: Rowena Ravenclaw

The Diadem of Ravenclaw was a beautiful, ancient-looking piece of jewellery described as a delicate, silvery tiara. It was tarnished with age when Harry Potter first encountered it. The diadem was set with a large, oval, faded-blue sapphire. Engraved upon its surface was the famous motto of Ravenclaw house: “Wit beyond measure is man's greatest treasure.” Despite its tarnished appearance in the Room of Requirement, its original beauty was legendary, and its ethereal quality was recalled by the ghost of Helena Ravenclaw.

The diadem was originally imbued with magic by its creator, Rowena Ravenclaw, to enhance the wisdom of its wearer. This was its primary and intended purpose, making it a highly coveted object for those seeking intellectual prowess. However, its nature was corrupted when Lord Voldemort turned it into one of his Horcruxes. By performing a murder and using powerful Dark Magic, he placed a fragment of his soul within the diadem. This act defiled the object and cursed it, while also granting it the extreme magical protection afforded to all Horcruxes. As a Horcrux, it could not be destroyed by conventional magical means and required a substance of immense destructive power, such as Basilisk venom or Fiendfyre, to annihilate the piece of soul it contained.

The diadem was created centuries ago by Rowena Ravenclaw, a founder of Hogwarts School of Witchcraft and Wizardry. Her daughter, Helena Ravenclaw, grew envious of her mother's intellect and status. Believing the diadem was the source of this wisdom, she stole it and fled to a forest in Albania. On her deathbed, a heartbroken Rowena Ravenclaw sent a man who loved Helena, the Baron, to find her and bring her home. The Baron tracked Helena to her hiding place in Albania, but when she refused to return, he killed her in a fit of rage. Overcome with remorse, the Baron then took his own life. The ghosts of Helena and the Baron returned to Hogwarts as the Grey Lady and the Bloody Baron, respectively. Before her death, Helena had hidden the diadem in the hollow of a tree. Centuries later, a young and charismatic Tom Riddle charmed the story of the diadem's location from the ghost of the Grey Lady. After leaving Hogwarts, he traveled to Albania, located the diadem, and turned it into a Horcrux by murdering an Albanian peasant. Believing he was the only one to have discovered the Room of Requirement's “room of hidden things” configuration, he later hid the diadem inside Hogwarts during a visit under the pretence of applying for the Defence Against the Dark Arts post. The diadem remained hidden for decades. Harry Potter unknowingly saw it in his sixth year while hiding his copy of Advanced Potion-Making, placing it on the head of a stone bust to mark the spot. During the Battle of Hogwarts, Harry, having learned of the diadem's nature as a Horcrux from the Grey Lady, realized what he had seen. He, Ron Weasley, and Hermione Granger went to the Room of Requirement to retrieve it. They were ambushed by Draco Malfoy, Vincent Crabbe, and Gregory Goyle. In the ensuing fight, Crabbe unleashed the uncontrollable cursed fire, Fiendfyre. The diadem was consumed by the magical flames, and the fragment of Voldemort's soul within was destroyed.

The Diadem of Ravenclaw served as one of Lord Voldemort's seven Horcruxes, making its discovery and destruction essential to his ultimate defeat. Its backstory provided a tragic history for the Ravenclaw house ghost, the Grey Lady, and the Slytherin house ghost, the Bloody Baron. The search for the diadem was a critical part of the final book, leading to a direct confrontation within Hogwarts during the climactic Battle of Hogwarts. Its hiding place in the Room of Requirement served to underscore Voldemort's immense arrogance, as he believed his knowledge of Hogwarts's secrets was unparalleled, yet Harry Potter had used the same room for his own purposes for years.

• In the film adaptation of Harry Potter and the Half-Blood Prince, the diadem is briefly shown when Harry hides his textbook in the Room of Requirement. (film)
• The method of the diadem's destruction is significantly different in the film Harry Potter and the Deathly Hallows – Part 2. After escaping the Fiendfyre, Hermione Granger stabs the diadem with a Basilisk fang obtained from the Chamber of Secrets, and Ron Weasley then kicks it into the receding flames. In the novel, the Fiendfyre alone is sufficient to destroy the Horcrux. (film)
• The diadem has appeared as a collectible item in various video games, including LEGO Harry Potter: Years 5-7. (video game)