A Horcrux is an object in which a Dark Wizard or witch has concealed a fragment of their soul. The appearance of a Horcrux is that of the object chosen to house the soul fragment. This can be any mundane object or an item of great magical or sentimental value. Lord Voldemort, the only known wizard to have successfully created more than one Horcrux, chose objects of significant historical or personal importance. Over time, the object housing the soul fragment becomes imbued with powerful and malevolent magic. It may exert a corrupting influence on those who come into contact with it, as seen with the locket's effect on Harry Potter, Ron Weasley, and Hermione Granger. A Horcrux can be a container for either an inanimate object, like a diary or a cup, or a living creature, such as a snake.
The primary and sole purpose of a Horcrux is to grant its creator a form of immortality. By tethering a piece of their soul to the mortal world, the creator cannot truly die, even if their body is destroyed. Their disembodied spirit can endure until they can create a new physical form.
The first known Horcrux was created by Herpo the Foul, an Ancient Greek Dark Wizard and one of the first known Parselmouths. The practice is mentioned in the book Magick Moste Evile, which calls it the “vilest of all magical inventions.” Lord Voldemort learned of Horcruxes during his time at Hogwarts School of Witchcraft and Wizardry from Horace Slughorn and the book Secrets of the Darkest Art. Believing the number seven to be the most magically powerful number, he planned to split his soul into seven pieces, creating six Horcruxes while the seventh part remained in his body. He became the only wizard in history known to have created more than one. His attempt to create a sixth Horcrux by murdering the infant Harry Potter backfired. The Killing Curse rebounded, destroying Voldemort's body and inadvertently splitting his already unstable soul a final time. This fragment latched onto the only living thing in the room, Harry Potter, turning him into an unintentional seventh Horcrux.
Horcruxes are the central plot device for the latter half of the series. After Albus Dumbledore discovers Voldemort's secret to immortality, he tasks Harry Potter with finding and destroying all of them. The quest to hunt the remaining Horcruxes forms the primary narrative of Harry Potter and the Deathly Hallows. The destruction of each Horcrux brings Voldemort one step closer to mortality, culminating in his final defeat during the Battle of Hogwarts. A comprehensive list of Lord Voldemort's Horcruxes is as follows: