A Horcrux is a dark magical object used to attain immortality. The concept is first introduced in Harry Potter and the Half-Blood Prince, though Horcruxes are present in earlier novels without being identified as such. The creation of a Horcrux requires one to commit a murder, which, as the supreme act of evil, "rips the soul apart". After the murder, a spell is cast to infuse part of the ripped soul into an object, which becomes the Horcrux. Rowling has never published the actual enchantment. In the final book of the series, Hermione finds the spell in a book titled Secrets of the Darkest Art.
Both inanimate objects and living organisms have been used as Horcruxes, though the latter are considered riskier to use, since an organism can move and think for itself. There is no limit to the number of Horcruxes a wizard can create. However, as the creator's soul is divided into progressively smaller portions, he loses more of his natural humanity and his soul becomes increasingly unstable. Under very specific conditions, a soul fragment can be sealed within an object without the intention or knowledge of the creator.
Horcruxes are extremely difficult to destroy. They cannot be destroyed by conventional means such as smashing, breaking, or burning. To be destroyed, a Horcrux must suffer damage so severe that repair through magical means would be impossible. Very few magical objects or spells are powerful enough to achieve this. Once a Horcrux is irreparably damaged, the fragment of soul within it is destroyed. A Horcrux can be magically undone only if the creator goes through a process of deep remorse for the murder committed to create the Horcrux. The pain of this remorse is so excruciating that the process itself may kill the creator.
Voldemort's creation of Horcruxes is central to the later storyline of the Harry Potter novels. As the number seven is a powerful, mystical number, Voldemort intended to split his soul into that many pieces, with six in Horcruxes and the last reposing within his body.
All of Voldemort's created Horcruxes were made using objects that had been important to him or that held some sentimental value.
Marvolo Gaunt's Ring
Tom Riddle created his first Horcrux using a ring owned by his maternal grandfather, Marvolo Gaunt, during the summer before his sixth year as a student at Hogwarts School of Witchcraft and Wizardry, when he was sixteen years old. He casts the spell after murdering his father. The ring is introduced during the fourth chapter of Half-Blood Prince, having already been destroyed by Albus Dumbledore, but its significance not yet revealed.
In a Pensieve memory, it is revealed that Riddle had taken the gold ring, which has a black stone inscribed with a magical symbol, from his uncle Morfin Gaunt, whom he had framed for the murder of his father and grandparents by altering his uncle's memories. Riddle wears the ring while still a student at Hogwarts, but eventually hides it in the house where the Gaunt family had lived. It remains hidden under the floorboards, placed in a golden box, and protected by several enchantments, until Dumbledore finds it during the summer break between the events of Order of the Phoenix and Half-Blood Prince. Dumbledore destroys the Horcrux with Godric Gryffindor's sword, though he is mortally injured by the ring's curses after putting the ring on his finger. The injury leaves his right hand permanently disfigured and would have killed him quickly if not for the intervention of Severus Snape, who slowed the curse to Dumbledore's right hand and arm, making them look withered, but the curse still progressed up Dumbledore's right arm and would eventually kill him if it had run its course. The damaged ring is kept for a time on a table in the Headmaster's office.
Before his death, Dumbledore hides the ring's black stone inside a Golden Snitch and he bequeaths the Snitch to Harry in his will. Dumbledore had learned that the stone is, in fact, the Resurrection Stone, one of the three Deathly Hallows. This was why he had put it on his finger: he had hoped to activate it and apologize to his long-dead family, quite forgetting it was also a Horcrux now, and thus likely to be protected by destructive enchantments. Voldemort remained unaware of the stone's additional magical properties throughout his lifetime.
Tom Riddle's Diary
Tom Riddle used his diary to create his second Horcrux during his sixth year at Hogwarts. He cast the spell after murdering his fellow classmate Moaning Myrtle using the Basilisk. The diary is introduced in the second chapter of the Chamber of Secrets and is destroyed by Harry Potter during the climax of the same book.
Before Voldemort's downfall, he entrusted the Horcrux to Lucius Malfoy. While aware of its corrupting magical properties, Malfoy did not know the diary was a Horcrux. In an attempt to discredit Arthur Weasley, Malfoy hid the diary in Ginny Weasley's cauldron, amidst her other books. Tom Riddle's soul-fragment possessed Ginny and, through her, reopened the Chamber of Secrets, finally starting to draw her life from her. At the end of book two, Harry saved Ginny and destroyed the diary by stabbing it with the venomous fang of a Basilisk, making it the first Horcrux to be destroyed. His reports of the diary's behaviour to Dumbledore were the latter's first inkling that Voldemort might have created not just one Horcrux, but several: "What intrigued and alarmed me most was that the diary had been intended as a weapon as much as a safeguard",implying that Voldemort must have had backups of some sort.
Helga Hufflepuff's Cup
Tom Riddle used a cup owned by Hogwarts founder Helga Hufflepuff to create his third Horcrux. The spell was cast after he murdered Hepzibah Smith by poisoning her. The cup is introduced during the twentieth chapter of Half-Blood Prince and is destroyed by Hermione Granger in the thirty-first chapter of Deathly Hallows.
Hepzibah Smith, who owned the cup, was a distant descendant of Helga Hufflepuff. Riddle killed Smith, stole the cup, then framed her house elf Hokey for the crime. Voldemort entrusted the cup to Bellatrix Lestrange, who kept it protected in her vault at Gringotts Bank, a place to which Harry guessed that a once penniless Voldemort would have always coveted a connection.
Salazar Slytherin's Locket
Riddle created his fourth Horcrux using a locket once owned by Salazar Slytherin, which had once belonged to Riddle's mother, Merope Gaunt. The spell was cast after Riddle murdered a Muggle tramp. The locket is introduced briefly in Order of the Phoenix (described only as "a heavy locket that not one of them could open") and is destroyed by Ron Weasley in the nineteenth chapter of Deathly Hallows.
Slytherin's locket was passed down through the generations and eventually ended up in the possession of Merope Gaunt. After being abandoned by her husband Tom Riddle Senior, Merope sold the locket to Caractacus Burke, shopkeeper of Borgin & Burkes, for ten galleons, a fraction of the locket's true value. The locket was eventually sold to Hepzibah Smith. Riddle stole the locket, along with Helga Hufflepuff's cup, after murdering Smith. Once the locket became a Horcrux, Voldemort hid it in a cave where he had once terrorized two of his fellow orphans. The cave's magical protection included a door that could only be opened with a blood offering, an enchanted boat, a basin of potion that causes pain and horrific visions to the drinker, and the use of Inferi. Dumbledore and Potter pursued the locket in The Half-Blood Prince, only to find a fake necklace.
Disillusioned Death Eater Regulus Arcturus Black had learned about the Horcrux and its hiding place beforehand. In an effort to bring about Voldemort's eventual downfall, he and his house elf Kreacher broke through the magical protection and stole the locket. While Black died in the effort, killed by the surrounding Inferi, Kreacher took the locket back to their home at Number Twelve, Grimmauld Place. Kreacher continued to protect the locket for years. However, while the Order of the Phoenix was using the house as its headquarters, the locket was stolen by Mundungus Fletcher, a petty criminal and member of the Order. He gave it to Dolores Umbridge as a bribe when she caught him selling stolen property.
Two weeks later, Harry, Ron, and Hermione infiltrated the Ministry of Magic where Umbridge worked, and stole the locket. Ron later saved Harry from being strangled by it when he wore it around his neck. When Ron attempted to destroy the locket, the fragment of soul inside assumed the shape of Harry and Hermione and played on Ron's fear that his two friends had started a romantic relationship during his absence. Ron destroyed the locket using the sword of Godric Gryffindor in the Forest of Dean.
After the release of the final book, several reviews noted similarities between Slytherin's locket and the One Ring from The Lord of the Rings, as both artifacts negatively affect the personality of those who wore them, are extremely difficult to destroy, and ensure their creator immortality.
Rowena Ravenclaw's Diadem
Lord Voldemort created his fifth Horcrux using Rowena Ravenclaw's diadem. A diadem is a kind of crown. Etched upon its surface was Ravenclaw's famous quotation: "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.
Nagini
Nagini is the snake that Voldemort has with him all the time. It is the only live Horcrux apart from Harry Potter. Voldemort uses the snake's milk for sustenance in Goblet of Fire before he is resurrected by Peter Pettigrew. This Horcrux was created by Voldemort when he was hiding in the forests of Albania; the victim of murder who led to its creation was Bertha Jorkins.
