The Diadem of Ravenclaw

• Type: Horcrux, Magical Tiara
• Owners: Rowena Ravenclaw, Helena Ravenclaw, Tom Riddle (Lord Voldemort)
• Maker: Rowena Ravenclaw

The Diadem of Ravenclaw was a beautiful, delicate tiara made of tarnished silver, shaped to resemble an eagle in flight. It was inlaid with a large, oval-shaped sapphire-like blue stone. Etched upon its surface was the famous motto of Ravenclaw house: “Wit beyond measure is man's greatest treasure.” When Harry Potter first encountered it, he noted it was ancient and beautiful, though it gave off a faint, dark aura, a testament to its corruption as a Horcrux. The Grey Lady described it as having been “tarnished by Dark Magic”.

The diadem's original and intended magical property was to enhance the wisdom of the wearer. This was the reason Rowena Ravenclaw's daughter, Helena, stole it, hoping to surpass her mother's renowned intellect. After being located by Tom Riddle, the diadem was cursed and transformed into one of Lord Voldemort's Horcruxes. This process involved Tom Riddle committing murder to split his soul and encasing a fragment within the object. As a Horcrux, it was protected by powerful Dark Magic and could only be destroyed by substances or spells of immense power, such as Basilisk venom or Fiendfyre.

The diadem was created by Rowena Ravenclaw, one of the four founders of Hogwarts School of Witchcraft and Wizardry. Her daughter, Helena Ravenclaw, grew envious of her mother's wisdom and stole the diadem, fleeing to a forest in Albania. On her deathbed, Rowena Ravenclaw wished to see her daughter one last time and sent a man who had long loved Helena to find her. This man, who would later become the Bloody Baron, tracked Helena to her hiding place. When she refused to return with him, he flew into a rage and murdered her. Overcome with remorse, the Baron then took his own life. Helena's ghost, who became known as the Grey Lady of Ravenclaw Tower, had hidden the diadem in a hollow tree just before her death, and its location remained a secret for centuries. During his years at Hogwarts, the charming and persuasive Tom Riddle coaxed the story from the Grey Lady. After leaving school, he traveled to Albania, located the diadem in the forest, and murdered an Albanian peasant to transform it into his fifth Horcrux. Believing he was the only person to ever discover the Room of Requirement's “room of hidden things” configuration, Voldemort returned to Hogwarts under the pretence of applying for the Defence Against the Dark Arts teaching position and hid the diadem there. He placed it atop the bust of an ugly warlock, confident it would never be found.

The diadem first appears, albeit unrecognised, in Harry Potter and the Half-Blood Prince. To hide his copy of Advanced Potion-Making from Professor Snape, Harry Potter enters the “room of hidden things” and places the book inside a cabinet. To mark the location, he places an old, dusty tiara on top of a warlock's bust. In Harry Potter and the Deathly Hallows, after learning from Dumbledore's memory that a Horcrux might be hidden at Hogwarts, Harry deduces it must be an artifact of Ravenclaw or Gryffindor. With help from Luna Lovegood, he identifies the lost Diadem of Ravenclaw as the most likely candidate. Harry seeks out and convinces the Grey Lady to reveal the diadem's history and its final resting place: within Hogwarts itself. Harry then remembers the tiara he used to mark his hiding spot and realizes it was the diadem. During the Battle of Hogwarts, Harry, Ron Weasley, and Hermione Granger enter the Room of Requirement to retrieve it. They are ambushed by Draco Malfoy, Vincent Crabbe, and Gregory Goyle. In the ensuing fight, Crabbe unleashes Fiendfyre, a cursed fire that he cannot control. The rampaging flames consume the room and, in the process, destroy the diadem, annihilating the piece of Voldemort's soul within it.

• In the film adaptation of Harry Potter and the Deathly Hallows: Part 2, the destruction of the diadem occurs differently. After retrieving it from the Room of Requirement, Hermione Granger stabs it with a Basilisk fang she and Ron Weasley retrieved from the Chamber of Secrets. Ron then kicks the inert Horcrux into the advancing Fiendfyre (film).
• While the book specifies the diadem is shaped like an eagle, the symbol of Ravenclaw house, many film-related materials and merchandise depict it with a raven, reflecting the house's name.