Spoil-o-meter: high
Horcruxes are great examples of dark magic. They were first introduced in the Harry Potter series, in Harry Potter and the Half-Blood Prince, the sixth book, although they appeared in books before the sixth. The Potions professor, Professor Horace Slughorn, gave Professor Dumbledore a memory (although Slughorn modified it, because he didn’t want to recall the real memory) of Tom Riddle, soon to be Lord Voldemort, (see White Witch vs. Lord Voldemort for more info about Riddle) asking him what a Horcrux was. Slughorn was very surprised that he asked this, because Tom was ‘such a good student.’ A Horcrux can be an animate or inanimate object, and even though Horcruxes are extremely dangerous to make anyway, making them with an inanimate object is safer than with a living organism, because the living organism can move, think, and talk for itself. Basically, you kill a person, which gives you the ability (with the help of a special spell, which J.K. Rowlings does not specify in her books) to split your soul in a dark way. The piece of soul goes into the animate or inanimate object, and stays there until it is destroyed, or taken back from it’s creator. Voldemort split his soul into seven different Horcruxes, because he thought that this would make him ‘immortal.’ The seven different Horcruxes are:
Tom Riddle’s Diary, in possession of Lucius Malfoy, later given to Ginny Weasley, and eventually found and destroyed by Harry in book two, Harry Potter and the Chamber of Secrets, with a basilisk fang. This Horcrux was created with the death of Moaning Myrtle.

Marvelo Gaunt’s Ring, hidden in the Gaunt Shack, found and destroyed by Albus Dumbledore in Harry Potter and the Half-Blood Prince, by Godric Gryffindor’s sword. This Horcrux was created with the death of Tom Riddle Senior. Note: This Horcrux doubles as one of the Deathly Hallows.

Salazar Slytherin’s Locket, hidden in a cave, later moved to 12 Grimmauld Place, stolen by Mundungus Fletcher and given to Dolores Umbridge in a bribe, found by Hermione and destroyed by Ron in book seven, Harry Potter and the Deathly Hallows, with Godric Gryffindor’s sword. This Horcrux was created with the death of a Muggle tramp.

Helga Hufflepuff’s cup, found by Harry, Hermione, and Ron, in the Lestrange family vault at Gringotts Wizarding Bank, destroyed by Hermione, in Harry Potter and the Deathly Hallows, with a basilisk fang. This Horcrux was created with the death of Hepzibah Smith.

Rowena Ravenclaw’s Diadem, found by Harry, Ron, and Hermione, in the Room of Requirement in Hogwarts School of Witchcraft and Wizardry, accidentally destroyed by Vincent Crabbe in Harry Potter and the Deathly Hallows, with Fiedfyre. This Horcrux was created with the death of an Albanian peasant.

Harry Potter himself, (part of his soul) destroyed (not Harry, but the Horcrux) by Voldemort before he knew that Harry was actually a Horcrux, in Harry Potter and the Deathly Hallows, Voldemort’s wand. This Horcrux was created with the death of Lord Voldemort. (It was possible, because that part of Voldemort’s soul was killed, but he still had other Horcruxes so that he wouldn’t die.)

Voldemort’s snake, Nagini, was always at Voldemort’s side after the cup was was stolen, so that Nagini (and Voldemort) wouldn’t die. It was destroyed by Neville Longbottom, in the entrance of Hogwarts school, beheaded with Godric Gryffindor’s sword. This Horcrux was made with the death of Bertha Jorkins. 
If you could make a Horcrux, what would you make it out of? Why?
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Works Cited: http://easybib.com/key/4d2df8