Horcruxes
A Horcrux is an object used to store part of a person's soul, protecting them from death. If the body of the Horcrux's creator is destroyed, the person is still able to survive, much the same way as Koschei in Russian folklore. When the body of a Horcrux owner is killed, that portion of his soul which had remained in his body will not pass on to the next world, but will rather exist in a non-corporeal form capable of being resurrected by another wizard, as in The Goblet of Fire. If all of someone's Horcruxes are destroyed, then his soul's only anchor in the material world would be his body, the destruction of which would then cause his final death.
This method was chosen by Voldemort 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. Rowling uses Horace Slughorn's expository dialogue to reveal that 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 then becomes a 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. Rowling has revealed that she intends to detail the process and spell used to create a Horcrux in her long-mentioned Harry Potter Encyclopedia.
Both inanimate objects and living organisms have been used as Horcruxes, though the latter are considered riskier to use, since a living being can move and think for itself. There is no limit to the number of Horcruxes a witch or wizard can create. However, as the creator's soul is divided into progressively smaller portions, he or she loses more of her or his natural humanity and the soul becomes increasingly unstable. Consequently, under very specific conditions, a soul fragment can be sealed within an object without the intention or knowledge of the creator. While the object thus affected will, like any Horcrux, preserve the immortality of the creator, it does not become a "Dark object". For example, Voldemort has unusual control over Nagini, and consequently Nagini is able to communicate with Voldemort about the presence of Harry in Godric's Hollow in Harry Potter and the Deathly Hallows.
Horcruxes made from inanimate objects 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 (mentioned and used were the Fiendfyre, Gryffindor's Sword and Basillisk fang). 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 can be so excruciating that the process 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 number in magic, Voldemort intended to split his soul into that many pieces, with six Horcruxes and the last piece reposing within his body. When Voldemort attacked the Potter family, he inadvertently created the sixth Horcrux, Harry. When his body was destroyed by the rebounded Killing Curse, a piece of his soul splintered off and attached itself to the only living thing remaining in the room – Harry Potter – making him a Horcrux. Later on, Voldemort, unaware of Harry being the sixth Horcrux, went on to complete his collection of the intended six Horcruxes by turning his snake Nagini into one, thus fragmenting his soul into a total of eight (counting the one residing in his own body), not seven, pieces. Complicating things even further, no more than six Horcruxes (including Harry) ever existed at any one time in the series: by the time Nagini had been made a Horcrux, one of the Horcruxes (Tom Riddle's diary) had already been destroyed.
All of Voldemort's deliberately created Horcruxes were made using objects that had been important to him or that held some sentimental value. He hid them carefully so that no one could find and destroy them, although Horcruxes cannot be destroyed by any means of wand usage or physical force. The exception to this rule is Fiendfyre, which destroyed the lost diadem of Ravenclaw in Harry Potter and the Deathly Hallows. In Harry Potter and the Chamber of Secrets, Harry intentionally destroys the diary with a Basilisk fang, although unaware it was a Horcrux at the time, to free Ginny from its influence.
Rowling revealed in Pottermore that Quirinus Quirrell served as a temporary Horcrux when Voldemort's soul possessed his body during Harry's first year at Hogwarts. A notable difference however is that the piece of soul within Quirrell was able to exist without its container, as it abandoned Quirrell and left him to die in the underground chambers. Based on this, the animals that Voldemort inhabited during his years of exile, such as rats and snakes, can also be considered as temporary Horcruxes.
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