A Horcrux is a powerful object in which a Dark wizard or witch has hidden a fragment of his or her soul for the purpose of attaining immortality.. Creating one Horcrux gives one the ability to resurrect oneself if the body is destroyed; the more horcruxes one creates, the closer one is to true immortality. Creating multiple Horcruxes is suggested to be costly to the creator, by both diminishing their humanity and even physically disfiguring them.
Creation of a Horcrux is considered the foulest act of Dark magic, as it attempts to violate and tamper with the multiple laws of nature and morality in its creation. Horcruxes are objects considered to be so evil that even the texts published explicitly to cater to the practise of the most terrible kinds of magic will not speak of them. Even Magick Moste Evile skirts the topic.
The only known book that provides specific instruction on the creation of a Horcrux is Secrets of the Darkest Art, once held in the Hogwarts Library. Due to the book's extremely dark and dangerous nature, Albus Dumbledore hid it away in his office; he did not destroy it, however.
The specific processes involved are known to involve a spell and a very horrible act. To split one's soul, one must also commit the most supreme act of evil — murder — and then encase a portion of their fractured soul into a chosen object with an as-of-yet unrevealed spell. The detached soul fragment will always remain as it was when it was divided; for instance, Tom Riddle's diary portrayed Tom Marvolo Riddle as a teenager while the eyes inside Salazar Slytherin's locket resembled Voldemort's eyes as they were back when he still had a relatively normal appearance.
- "This is the one that gives explicit instructions on how to make a Horcrux. Secrets of the Darkest Art – it’s a horrible book, really awful, full of evil magic… And the more I've read about them, the more horrible they seem, and the less I can believe that he actually made six. It warns in this book how unstable you make the rest of your soul by ripping it, and that’s just by making one Horcrux!"
- —Hermione Granger on researching how Voldemort made Horcruxes[src]
Though a Horcrux can be made from anything, Lord Voldemort chose to use objects of great significance or importance. The process makes the part of the soul remaining in the witch or wizard unstable. If the maker's physical body is later destroyed, he or she will live on in non-corporeal form, although there are methods of regaining physical form. However, according to Horace Slughorn, few would want to live in such a form and death would be preferable.
It is stated at one point that Voldemort had already "pushed his soul to the limit" in creating his seven Horcruxes. This implies a finite number of Horcruxes any one person may create before the process becomes too dangerous to attempt again. Though this limit is never explicitly stated, the number seems to set solidly at seven intentional Horcruxes, and creating seven Horcruxes in addition to the person's own body renders the soul unstable and liable to break off when the person whose soul it is commits murder. Dumbledore explicitly stated that Voldemort's soul had become so unstable that it finally "broke apart" when Voldemort tried to murder Harry for the first time.
- Ron: "Isn’t there any way of putting yourself back together?"
- Hermione: "Yes, but it would be excruciatingly painful."
- Harry: "Why? How do you it?"
- Hermione: "Remorse. You’ve got to really feel what you’ve done. There’s a footnote. Apparently the pain of it can destroy you. I can’t see Voldemort attempting it somehow, can you?"
- — Ron Weasley, Harry Potter and Hermione on reconciling the fragments of a broken soul[src]
The creation of a Horcrux can be reversed by its creator by truly feeling remorse, though the effects of this can apparently be painful to the point of being fatal. However, as described below, this may be a far preferable outcome than the alternative.
Interestingly, since Dumbledore said that "there is no help possible" for Voldemort's soul, it may be that any soul as badly damaged as Voldemort's could no longer be repaired through remorse as described in Secrets of the Darkest Art. Alternately, and more likely, the soul can still be repaired through the redemptive power of repentance. Harry told Voldemort to "try . . . be a man. . . try for some remorse. It's your one chance. It's all you've got left." This seems to indicate that though Tom Riddle's soul is maimed and seriously injured, he can still repair it by regretting all the horrible things he did, as Gellert Grindelwald did later in life.
- Harry: "So if all of his Horcruxes are destroyed, Voldemort could be killed?"
- Dumbledore: "Yes, I think so. Without his Horcruxes, Voldemort will be a mortal man with a maimed and diminished soul. Never forget, though, that while his soul may be damaged beyond repair, his brain and his magical power remain intact. It will take uncommon skill and power to kill a wizard like Voldemort, even without his Horcruxes."
- — Harry and Dumbledore discussing how to destroy Voldemort[src]
Horcruxes can also be destroyed by others, seeing as the piece of the soul depends upon its container to survive; the opposite of a human being. Destruction of a Horcrux is difficult, but not impossible, and requires that the receptacle to be damaged completely beyond physical or magical repair. When a Horcrux is damaged to this point, it may appear to "bleed" (ink in the case of Tom Riddle's Diary and a "dark blood-like substance" in the case of Ravenclaw's Diadem) and a scream may be heard as the soul fragment perishes. Dumbledore's blackened hand after destroying a Horcrux.Added by QuibblerGalIt is unknown if the creator of the Horcrux will be able to sense that his soul fragment was destroyed, although Dumbledore stated that in the particular case of Voldemort, he wouldn't feel their loss because his soul was sliced too many times and stayed that way for too long.
All known methods of Horcrux destruction are as deadly as the creation. For example, the earliest known method is administering basilisk venom to the Horcrux, the procurement of which is next to impossible. Other known methods are Fiendfyre (as evidenced by its destruction of Rowena Ravenclaw's Diadem), which requires extreme skill to control and the Killing Curse (extremely Dark magic) which seems to be capable of destroying a Horcrux if it is animate, given that part of Voldemort's soul contained in Harry Potter was destroyed when he was struck with the Killing Curse in 1998. However, Harry Potter was never a true Horcrux (see below) and so it may not work on a proper, animate Horcrux (like Nagini), probably having unforeseen side effects.
Albus Dumbledore, Ron Weasley, and Neville Longbottom used Godric Gryffindor's Sword to destroy Marvolo Gaunt's Ring, Salazar Slytherin's Locket, and Nagini respectively. This was only achievable as the sword is a Goblin-made artefact, which can absorb qualities that strengthen it. When Harry Potter slew the Basilisk in the Chamber of Secrets, the sword was imbued with Basilisk venom and became capable of destroying Horcruxes.
The fragments of a person's soul within a Horcrux can think for themselves and have certain magical abilities, including the ability to influence those in their vicinity. When Harry, Ron, and Hermione were carrying Salazar Slytherin's Locket around their necks in 1997, they each became moodier and more prone to fighting, especially Ron. They were also unable to summon their Patronuses while wearing the locket since the soul fragment inside was darkening their thoughts. A person with an affinity for the Dark Arts, on the other hand, would be strengthened by the influence of a Horcrux, as Dolores Umbridge was when wearing Salazar Slytherin's Locket. If a person is more emotionally vulnerable, it is possible for the soul inside the Horcrux to take control of him or her, as Tom Riddle's Diary did to Ginny Weasley. In fact, Voldemort took advantage of this possessive power to reopen the Chamber of Secrets, using the diary as a weapon rather than a safeguard.
In this way, a Horcrux can gradually feed on another person's life or negative emotions to strengthen itself and increase the ability of the soul fragment within to act independently in the physical world. The best example of this is in the case of Tom Riddle's diary. For decades, the diary lay dormant in Lucius Malfoy's possession, doing nothing other than safeguarding the soul fragment of Tom Riddle. When Ginny Weasley began to transcribe her fears and insecurities into the pages of the diary, the fragment of Tom Riddle's soul contained within was not only able to write back to Ginny but eventually drained enough life out of her to actually manifest itself in a semi-corporeal form and work magic with Harry Potter's wand. Likewise, Salazar Slytherin's Locket slowly gained power when it was in the possession of Harry, Ron, and Hermione in the months prior to its destruction. It can be theorized that the locket gained somewhat less power from them (not enough for Riddle to fully manifest but still enough to speak and create illusions) because Harry, Ron, and Hermione were actively resisting the locket's influence instead of embracing it as Ginny had done with the diary. On the other hand, Horcruxes which have been isolated for long periods of time (such as Hufflepuff's Cup and Ravenclaw's Diadem) were very passive by comparison and took no real measures to protect themselves. Even Slytherin's Locket was fairly inert when it was initially discovered in a cabinet in the drawing room at 12 Grimmauld Place, displaying no powers other than being impossible to open.
Horcruxes also possess some last line of defence against destruction. The fragment of soul within the Horcrux seems to be able to sense impending threats and can act to defend itself. For instance, Slytherin's locket viciously taunted Ron Weasley with visions of his deepest fears and even attempted to strangle Harry Potter.
To create a Horcrux is to divide one's soul - the "essence of self" - and it is therefore in the creation of a Horcrux that one falls prey to Adalbert Waffling's first Fundamental Law of Magic, which essentially states that tampering with one's soul inevitably results in grave side effects.
One of these such side-effects is the "dehumanising" effect the mutilation of one's soul is said to have. The more Horcruxes one creates, the less human they become, both emotionally and physically; for example, in the house-elf Hokey's memory Tom Riddle is initially shown to be hollow-cheeked but otherwise normal, though ten years later his features look as if they have been burned and blurred, and his skin is extremely white. One can hence assume that during those ten years he had created more than one Horcrux that in turn wrought the physical changes in Voldemort over that timespan.
Of course, this initial consequence of dehumanisation has its own side effect; it logically follows that if one becomes dehumanised by Horcrux creation then they will take less stock of morality in general, increasing the likelihood that they will create another Horcrux, which would in turn make them less human and hence less moral, which further increases their likelihood of making more Horcruxes and so on. In other words, Horcrux creation may be thought of as a "slippery slope" or "downward spiral" until one reaches the limit, at which point no more Horcruxes may be made.
One should note that it is unclear whether the red eyes and slit-like nostrils that Voldemort has after he is reborn are caused by having more Horcruxes than he did than when he applied for the Defence Against the Dark Arts post a second time, or whether they are characteristics of a person who has been resurrected with the help of serpents (who have continued to play key roles in his revival). It is probable that he performed these transformations prior to his resurrection as all of his Death Eaters seem to recognise him without question after Voldemort returned.
A third side effect of Horcrux creation is that the Master Soul itself becomes unstable (even with creating just one Horcrux). The precise dangers of this spiritual destabilization are not currently detailed explicitly throughout the franchise, however, some can be gleaned from the events in the books. For example, the creation of Voldemort's seventh "Horcrux" - Harry Potter - is known to be the direct result of this as when Voldemort was hit by the back-fired Killing Curse at his parent's home in Godric's Hollow it caused his soul to split, with one fragment remaining in him and the other displaced part immediately seeking out the only other living thing in the room and latching onto it - Harry Potter. However, one should note that although this parasitic fragment of Voldemort's soul attached to Harry's has been mistaken for a Horcrux it has been confirmed that in actuality it does not truly constitute one, since it was not created intentionally. Likewise, not all of the known parts of the Horcrux creation process were correctly carried out for it. Voldemort had just committed 2 murders (Harry's parents) so that may have been adequate for that requirement. In this state, Harry Potter may be more accurately described as a "proto-Horcrux", though for simplicity he may be termed a Horcrux regardless.
The final known side-effect of Horcrux creation is the inability to move on from Limbo after death. This is seen when Voldemort's Killing Curse (after the destruction of all the other Horcruxes) rebounded and finally ended his life once and for all, his broken and mangled soul was forced to exist in the stunted form of a flayed and mutilated baby that Harry saw in King's Cross during his visit to Limbo, unable to return to the land of the living, unable to become a ghost, and unable to go to the land of the dead because his soul was maimed and unwhole. Reconciliation cannot occur after death, as the soul's state at death remains forever, so the greatest of all consequences incurred by Horcrux creation may be the possibility of eternal limbo of the soul.
Role in the series
The method of creating a Horcrux has been discovered by Chernabog's apprentice, Malefor, who split Cobra's soul into several different villains as punishment for failing him once again. The villains that were given a piece of Cobra's soul were Master Xehanort, Vanitas, Terranort, Ansem SOD, Xemnas, and Sora's Heartless, and an currently undiscovered one. Currently, most of the Horcruxes have been destroyed by Sora and Spongebob's efforts, but now only one remains.