Theft of Rowena Ravenclaw's Diadem

"I stole the diadem. I sought to make myself cleverer, more important than my mother. I ran away with it. My mother, they say, never admitted that the diadem was gone, but pretended that she had it still. She concealed her loss, my dreadful betrayal, even from the other founders of Hogwarts."

- Helena Ravenclaw

The theft of Rowena Ravenclaw's diadem took place in the Founders' time (in around the early 1000s). Helena Ravenclaw, the daughter of the Ravenclaw House's Founder Rowena Ravenclaw, was jealous of her mother's wisdom and fame. She wanted to be cleverer and more famous than her mother, so she stole her mother's Diadem and escaped. Rowena, who was badly ill, ordered the Baron, a bad-tempered man who loved Helena, to find her daughter. However, when the Baron found Helena in a forest at Albania, she refused to go back with him. The Baron killed her in rage. After seeing what he had done, remorseful of his action, he stabbed himself to death.

Background information
Rowena Ravenclaw's Diadem (also known as the Lost Diadem of Ravenclaw) was the only known relic once belonging to Rowena Ravenclaw, the founder of Ravenclaw House at Hogwarts School of Witchcraft and Wizardry. Etched upon its surface was Ravenclaw's famous quote: "Wit beyond measure is man's greatest treasure." It was said to enhance the wisdom of its wearer, which is Ravenclaw House's most treasured attribute. It has a blue sapphire shaped like an oval.

As Rowena Ravenclaw was a very intelligent woman, it is most likely she enchanted the diadem herself, putting a charm on the object to increase the wearer's intelligence.

The theft and attempted retrieval
Helena Ravenclaw, Rowena's daughter, greatly envied the attention her mother received. She stole her mother's diadem, in hope of using its power to make herself wiser, and fled Hogwarts. Her mother fell fatally ill and in spite of Helena's betrayal, wanted to see her daughter one last time. Rowena sent the Bloody Baron, a man who once loved Helena, to find her.

When he caught up with her in a forest in Albania (the same forest Lord Voldemort would use as a hiding place during his exile), she hid the diadem in a hollow tree. Upon her refusal to return with him, the Baron stabbed her in his anger and jealousy (because Helena was free now); horrified by what he had just done, the Baron then stabbed himself as well.

They both transformed into their House Ghost after death. During a thousand years afterwards, loads of students asked "the Grey Lady" Helena Ravenclaw about where the diadem was because they wanted to get good marks in exams.

Tom Riddle's Plot
"I know who he is! I know what he's done! He defiled it - with Dark magic!"

- The ghost of Helena Ravenclaw to Harry Potter

Centuries later, Tom Marvolo Riddle managed to charm the story out of Helena's spirit, then known as the Grey Lady, ghost of the Ravenclaw house. Upon learning of the diadem's location, Riddle travelled to the Albanian forest shortly after he left school and acquired the diadem. He transformed it into his fifth Horcrux by killing an Albanian peasant, and later chose to return it to the very place it had originated from: Hogwarts.

Riddle was arrogant enough to believe that he alone had penetrated Hogwarts' most mysterious secrets, and thus he believed that only he had discovered the Room of Requirement, where he intended to hide the diadem. The Room's manifestation was none other than the "Room of Hidden Things" inside which Harry Potter would hide the Half-Blood Prince's copy of Advanced Potion-Making many decades later. Riddle chose to hide the diadem in this room the night he returned to the castle to request a position to teach Defence Against the Dark Arts. Unlike the other Horcruxes, Riddle did not put up heavy magical protections for the diadem, due to his lack of time to do so, along with his arrogance.

Search for the diadem
In 1998, while the Battle of Hogwarts raged on, Harry thought about possible locations of the Ravenclaw-related Horcrux. All anyone seemed to associate an object of Ravenclaw to was the Lost Diadem, but no one had seen the diadem in living memory. At this thought, Harry decided to ask a ghost, as they have been around much longer than anyone else. Harry found Nearly Headless Nick, and asked him where he might find the Ravenclaw house ghost. Somewhat miffed that Harry did not want his help, Nick indicates The Grey Lady, and Harry eventually chased her down and asked if she knew anything about the diadem. After gaining her trust, she revealed that, during her life, she was Rowena Ravenclaw's daughter, Helena, and she stole the diadem from her mother to make herself cleverer.

She revealed that she hid the diadem in a hollow tree in a forest in Albania, and she also ashamedly admitted to having told one other student about it, many years before. Harry privately thought that the Grey Lady is only one of the many who had been hoodwinked by Tom Riddle's charms. Harry put together that Voldemort found the diadem in Albania, and brought it back to Hogwarts to hide it the night he asked Dumbledore for the Defence Against the Dark Arts job. Harry then remembered that Voldemort operated alone and may have been arrogant enough to think that he alone discovered Hogwarts secret of the Room of Requirement. Harry knew immediately that Voldemort had hidden the Lost Diadem there.

Returning to the Room of Requirement, Harry found Ron and Hermione there. They informed him that Ron had opened the Chamber of Secrets by mimicking the Parseltongue language Harry had made to open the Locket Horcrux, and Hermione had recovered several Basilisk fangs, using one of them to destroy Helga Hufflepuff's Cup, one of the Horcruxes and recovering the others to destroy any future Horcruxes that they found. Reunited, the trio then entered the Room of Requirement, which Harry had re-opened as the junk storage warehouse where Voldemort had placed the diadem. However, Draco Malfoy, Gregory Goyle and Vincent Crabbe appeared and tried to stop the trio.

Destruction of the diadem
Draco wanted to take Harry and the diadem to Voldemort, but Crabbe and Goyle wanted to kill Harry. Crabbe even casted a dangerous Dark Magic known as Fiendfyre. It destroyed the diadem and evantually killed Crabbe himself as well. Harry took out the diadem and saved Draco and Goyle. However, the diadem was ultimatly destroyed by the fire.

"A bloodlike substance, dark and tarry, seemed to be leaking from the diadem. Suddenly Harry felt the thing vibrate violently, then break apart in his hands, and as it did so, he thought he heard the faintest, most distant scream of pain, echoing not from the grounds or the castle, but from the thing that had just fragmented in his fingers."

- Description. After that, five Horcruxes had now been destroyed.

Behind the scenes

 * Harrypotter7part2photo2.jpg the second film adaption of Harry Potter and the Deathly Hallows in which the Grey Lady tells Harry where to find the Ravenclaw Diadem, Helena's back-story of stealing the diadem from her mother, her history with the Bloody Baron, Rowena sending the Baron after her, and the Baron eventually killing Helena and then committing suicide, is never explained. Harry seems to already know that the Grey Lady's real name is Helena Ravenclaw, implying that her history is already well-known to Hogwarts students, while in the book, it is implied that no-one, or at least very few, students are aware of this fact. Rather than merely regretful and saddened by the Diadem's conversion into a Horcrux, Helena appears greatly offended and angered by this fact, which is evident when she shouts to Harry, "I know who he is! I know what he's done! He defiled it with Dark Magic!"
 * In the book, after talking to Helena, Harry encounters Hagrid and Fang, who had been sent crashing in through a nearby window by Grawp. They then set to look for Hermione and Ron, who they find having just returned from the Chamber of Secrets, which they tell Harry about Ron's idea when asked where they've been. Harry does not see Hagrid after talking to Helena in the film, and Ron and Hermione's whereabouts are not of concern, as they told him of Ron's idea before heading to the Chamber.

Appearances

 * Harry Potter and the Deathly Hallows
 * Harry Potter and the Deathly Hallows: Part 2