Horcrux

A Horcrux is an object of extremely Dark Magic. Described in Magick Moste Evile as "the wickedest of all magical inventions", it is defined as any object which contains a part of an individual's soul.

Nature of a Horcrux
The book Secrets of the Darkest Art, in the Hogwarts Library, gives explicit instructions on creating Horcruxes. However, this specific information is unknown to this encyclopedia. What is known is that to split one's soul, one must first commit the most supreme act of evil - murder - and then encase a portion of their fractured soul into a chosen object. The chosen object is usually one of great signicifance or importance, as this act can only be reversed through acts of remorse that are physically very painful.

The process violates two laws of nature and common human decency laws. The first is that mankind must not commit such acts upon one another. The second is that one's soul must remain whole and intact. For these reasons, the Horcrux is the most unnatural and dark magical object. What's more, the subject of Horcruxes is banned at Hogwarts School of Witchcraft and Wizardry.

A Horcrux is the opposite of a human being, in that the piece of soul depends upon its container to survive. Destruction of a Horcrux is difficult, but not impossible, and requires that the object be damaged beyond magical repair. One of the most foolproof methods of destruction is Basilisk venom. Very few other methods work, but among methods known are breaking the Horcrux with a magical weapon, such as Godric Gryffindor's sword, or through a magical smelting procedure, such as with Fiendfyre.

Horcruxes can also be enchanted to provide some line of defense against destruction. For instance, a spell that makes the object appear too beautiful to destroy, instilling the attacker with great fear and despair, or even direct violence against the attacker.

Horcruxes of Lord Voldemort
Lord Voldemort, obsessed with immortality, went further than any wizard known to history to create seven seperate parts of his soul. As a student named Tom Marvolo Riddle, he learned of Horcruxes from some source during his tutilage at Hogwarts, and sought out Potions Master Horace Slughorn for further information. At some point after that, Slughorn informed Dumbledore of their discussion, and gave him a partial stored memory of it. After that, all books regarding Horcruxes in the Hogwarts School Library were confiscated and stored in the Headmaster office, until Hermione Granger absentmindedly summoned them to her dormitory at the end of the 1996 school year.

Decades later, Dumbledore and Harry Potter embarked on a quest to locate and destroy, in secret, what they believed to be as many as six to seven of Voldemort's Horcruxes.

List of Horcruxes
Although Voldemort had seven Horcruxes, no more than six existed at one time because Tom Riddle's diary was destroyed before Nagini was made into a Horcrux. As Albus Dumbledore stated, using a living being as a Horcrux is treacherous, as the creature could die and the Horcrux lose its integrity.

Parallels in the Muggle World
However, the concept of a "soul container" is not original to the world of Harry Potter. For example, the legendary undead Lich could maintain immortality by concealing regeneration power in a phylactery. The Russian myth of Koschei the Deathless is another. In Native American folk tales, sorcerers could evade death by sealing their spirit inside parrots, becoming invulnerable until the parrot was destroyed. In Tolkein's Lord of the Rings series, the Dark Wizard Sauron stored his power and ability to maintain physical form in The One Ring.