A Horcrux is an object in which a wizard or witch has concealed a fragment of their soul in order to attain immortality. The process of creating a Horcrux is considered the foulest act of Dark Magic, as it involves splitting one's soul through murder and then using a spell to encase the torn portion within a chosen object. Any object, or even a living being, can be turned into a Horcrux. Lord Voldemort, the most prolific creator of Horcruxes, chose objects that held great historical or personal significance to him. The object itself does not necessarily change in appearance, but it becomes imbued with powerful Dark Magic and is exceptionally difficult to destroy. Horcruxes can also exert a powerful, corrupting influence on those who possess or come into close contact with them for extended periods.
The primary purpose of a Horcrux is to anchor its creator's soul to the mortal plane. If the creator's body is destroyed, they will not die but will continue to exist in a non-corporeal, “less than spirit” form. From this state, they can eventually be returned to a physical body through powerful and complex Dark Magic. The creation process has several profound effects:
Destroying a Horcrux is extremely difficult. The container must be damaged to an extent that it is beyond any form of magical repair. The only two substances known to be capable of this are Basilisk venom and Fiendfyre. The Sword of Gryffindor, by virtue of having been used to kill a Basilisk, became imbued with its venom and could therefore also destroy Horcruxes. A living Horcrux can be destroyed if its host is killed in a way that is irreparable. In the unique case of Harry Potter, the soul fragment within him was destroyed by the Killing Curse cast by its original owner, Lord Voldemort, without killing Harry himself due to the protection of his mother's sacrifice.
The concept of the Horcrux was first pioneered by Herpo the Foul, who successfully created one. The knowledge was recorded in books on the foulest of Dark Arts, such as Secrets of the Darkest Art, which Albus Dumbledore later removed from the Hogwarts Library. The most infamous user of this magic was Lord Voldemort. As a student at Hogwarts, Tom Riddle learned of Horcruxes from Professor Slughorn. Believing seven to be the most powerfully magical number, he planned to split his soul into seven pieces by creating six Horcruxes, with the final piece residing in his own body. He ultimately created seven Horcruxes, though the final one was unintentional. Lord Voldemort's Horcruxes were:
The existence of Lord Voldemort's Horcruxes is the central secret of the latter half of the series and the driving force of the plot in Harry Potter and the Deathly Hallows. After Albus Dumbledore confirmed their existence and number through his research and recovered memories, he tasked Harry Potter with finding and destroying them all. This “Horcrux hunt” became the primary mission for Harry, Ron Weasley, and Hermione Granger following Dumbledore's death. The destruction of each Horcrux was a critical victory, slowly dismantling Voldemort's immortality and making him vulnerable. Only after all the Horcruxes were destroyed could Lord Voldemort finally be defeated.
The name “Horcrux” is likely a portmanteau created by J.K. Rowling.
Together, the name can be interpreted as “horror-cross” or “pivotal horror,” aptly describing an object that is both horrific in nature and central to the plot to defeat Lord Voldemort.