In Harry Potter, a Horcrux is the name given to an object containing part of a wizard's soul hidden by himself to gain immortality. Creating one Horcrux gives one the ability to anchor one's own soul to the world of the living if the body was destroyed, giving them chance to re-created a new body. The more Horcruxes one created, the closer one was to true immortality. Creating multiple Horcruxes was suggested to be costly to the creator, by both diminishing their humanity and even physically disfiguring them to the point that they not only become eviler, but also turned into a humanoid abomination of their former selves.
This concerns the Horcruxes in general as well as the most famous ones that used to sustain the life of the Harry Potter franchise's main villain Lord Voldemort.
In the Harry Potter series, Horcrux was said to be invented by Herpo the Foul, the same Dark Wizard whom invented the means to create a Basilisk snake. The other known Horcrux creator was Lord Voldemort, whom become the first and possibly the only known wizard whom create more than 6 Horcrux. Aside both of them, it was suggested that there were few other wizards whom also create their own Horcruxes, as Horace Slughorn mentioned that the fate of those who used Horcruxes to survive was what only few would prefer.
The nature and concepts of Horcruxes were so terrifying, they were kept secret from most of the wizarding world, and only few ever knew what they were. Hogwarts banned the subject of Horcruxes, and even books such as Magick Moste Evile only skimmed the subject, at best. The only known book that explained Horcruxes in detail was Secrets of the Darkest Art. As little was known of the subject at that time, no one knew what the effects of creating more than one Horcrux would be, because, aside from Voldemort, nobody had done so.
By the time Harry Potter sacrificed himself to destroy a piece of Voldemort's soul inside him by allowed the Dark Lord killed him via Killing Curse but thanks to both sacrifical protection that has been put by his late mother and the said soul's piece resulting his sould wind up in Limbo and had the chance to return to life, it was revealed that by shredding one's soul includes for creating Horcrux resulting his/her mangled spirit would forced to exist in the stunted form of a flayed and mutilated baby-like entity, 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/her soul was maimed and unwhole. It is unknown if this was either a standard fate meted out for all Horcrux creators, or if it was unique to Voldemort due to the number of his Horcruxes.
A Horcrux is created by placing a piece of a wizard's spirit into an object that he/she wishes to converted into. In order to split the soul for creating a Horcrux, he/she must commit the act of murder as killing someone rips the soul apart. The rest of the Horcrux creation process is unknown, other than having a spell involved which used to encase a portion of their fractured soul into a chosen object. The detached soul fragment would always remain as it was when it was divided: Should the piece of soul inside a Horcrux manifests into physical being, it would manifests as the form of creator itself during the time they create that Horcrux and the object that converted into a Horcrux would gained some elements of its creator's physical appearance. The instance was when Voldemort manifests from his diary that has turned into one of his Horcrux, he manifests as his teenage self when he converted it. Other instance would be eyes inside Salazar Slytherin's Locket resembled Voldemort's eyes as they were when he looked more human.
While the soul that remained in the creator's body become unstable due to some of them used for Horcrux construction, he/she would live in non-corporeal form should his/her body destroyed, although there were methods of regaining physical form.
It appeared that there are a finite number of Horcruxes any one person may create before the process became too dangerous to attempt again. Though this limit was never explicitly stated, the number seemed to be set solidly at seven intentional Horcruxes, and creating seven Horcruxes in addition to the person's own body rendered the soul unstable and liable to break off when the person whose soul it was committed murder. Dumbledore explicitly stated that Voldemort's soul had become so unstable that it finally "broke apart" when Voldemort tried to murder Harry Potter for the first time on October 31, 1981 in Godric's Hollow, where Lily's sacrifical protection that done to protect Harry causes a piece of the Dark Lord's soul wind up entered Harry's body and accidently turned him into a Horcrux.
Horcruxes can be destroyed only by some specific ways, otherwise, it will regenerate. If a person's body was destroyed, his or her soul would remain intact, whereas with a Horcrux, it was the opposite, as the piece of soul depended upon its container to survive. The destruction of a Horcrux was difficult, but not impossible, and required that the receptacle to be damaged completely beyond physical or magical repair. When a Horcrux was damaged to that 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 perished. However, as a safety measure to protect one's immortality and precious soul fragment, the creator would usually place powerful enchantments onto the artefact to prevent damage, to the point where the most powerful house-elf magic would not succeed.
It was unknown if the creator of the Horcrux would be able to sense that his soul fragment was destroyed, although Dumbledore stated that in the particular case of Voldemort, he would not feel their loss because his soul was split too many times and stayed that way for too long. However, this was completely reversed in the movies: That is the reason Voldemort starts on the journey of seeing if all the Horcruxes are safe in the books, but in the movies it is unclear if he even checks his hiding spots. When Hermione destroys the Hufflepuff Cup, Voldemort, Harry and Nagini all seem to be momentarily incapacitated by pain. This also happens when the Ravenclaw Diadem and Nagini are destroyed, clearly showing that all Horcruxes and the Master Soul feel the destruction of the others.
The following means to destroyed Horcruxes includes:
- Basilisk Venom: Its shown in the Harry Potter series as the strongest snake poison, being able to destroy magical things and to kill a human in minutes (it almost killed Harry in the second movie/book, but he was healed by Fawkes the phoenix), Basilisk Venom is powerful enough to destroy a Horcrux. The first display on Horcrux's destruction with Basilisk Venom was when Harry used the giant snake's poisonous fang to destroyed Riddle's Diary. Hermione later used one to destroyed Hufflepuff's Cup.
- Godric Gryffindor's Sword: The Sword was made by goblins with a special metal that absorbs anything that strengthens it. When Harry used Gryffindor's Sword to kill the Basilisk, the Sword absorbed the monster's poison, resulting it able to destroy Horcruxes. In the series, Gryffindor's Sword is used to destroy Gaunt's Ring, Slytherin's Locket, and Nagini.
- Fiendfyre: A cursed fire that can be cast by a very advanced spell. It cannot be put out by water and it burns faster than normal fire, its high destructive power can destroy Horcruxes and other powerful magical objects. In the series, the Fiendfyre destroys Ravenclaw's Diadem.
- Killing Curse: Killing Curse (incantation: Avada Kedavra) is the most powerful of the three forbidden curses, and can cause instant death to someone in which its cast. Since the Horcrux is nothing more than a part of a soul, it is vulnerable to Avada Kedavra. In the series, the Death Curse is cast on Harry, destroying the Horcrux within him and giving him the option to return after his death, since he had more than one soul.
- Remorse: A Horcrux can be destroyed if a witch or wizard who created the Horcrux feels true remorse for his or her actions. However, the process is considered quite painful and it is stated that the witch or wizard could die from it. Since Lord Voldemort has never showed any remorse for his actions, none of his Horcruxes were destroyed by this.
Lord Voldemort's Horcruxes
Seven were made by Lord Voldemort to keep himself immortal; 6 that he created intentionally using objects that he considered valuable and one that he accidentally created, which was Harry Potter himself, when Voldemort tried to kill him as a baby.
Tom Riddle's Diary
The Diary was the first Horcrux to be destroyed and the first to be created. It was created from the murder of Moaning Myrtle. It was destroyed by Harry Potter himself in the series in the second movie/book Harry Potter and the Chamber of Secrets. The diary was chosen by Voldemort to be an Horcrux because it was what bonded him to Hogwarts. It was secretly given to Ginny Weasley by Lucius Malfoy where neither of them aware with it's nature as Horcrux. Ginny, by writing in the diary, discovered that he could answer her, and started to tell her secrets, making her open her heart to him. Riddle's Diary then, started to control her and make her order his Basilisk to attack the students that weren't considered pure-blood; in other words, anyone that had muggle blood. When Harry descend to the Chamber of Secrets, the Diary orders the Basilisk o kill him. After Harry's victory against the monster, he used its poisonous fang to destroy the Diary's Horcrux.
Marvolo Gaunt's Ring
The Ring was the second Horcrux to be destroyed. It was created from the murder of Voldemort's paternal family (Thomas Riddle, Mary Riddle, and Tom Riddle Sr.)It was destroyed by Albus Dumbledore in the events between the fifth and the sixth movies/books Harry Potter and the Order of Phoenix and Harry Potter and the Half-Blood Prince. It was chosen by Voldemort to be an Horcrux because it belonged to his family and it was once from Salazar Slytherin, what bound him to nobility, even that he was a half-blood. Dumbledore destroyed it with Godric Gryffindor's Sword that absorbed the Basilisk's poison when Harry killed the monster with it. The Ring was protected by a curse that affected Dumbledore and would eventually cause his death.
Salazar Slytherin's Locket
The Locket was the third Horcrux to be destroyed. It was created from the murder of a muggle tramp. It was destroyed by Ron Weasley in the last book Harry Potter and the Deathly Hallows, and in the first part of its movie adaptation. It was chosen by Voldemort to be an Horcrux because it was from the great wizard Salazar Slytherin. The Locket was taken by Regulus Arcturus Black from its hiding place and left by Kreacher who tried to destroy it in vain. When Harry gone to the hiding place he found a fake of the Locket with "R.A.B." written in it. After discovering who was R.A.B. (Regulus) he asked Kreacher to find Mundungus Fletcher who stole it from the No. 12 Grimmauld Place. Then Dolores Umbridge took the Horcrux as a bribe from Fletcher and kept it on herself. Harry and his friends sneaked into the Ministry in disguise, stunned Umbridge, took the horcrux, and escaped from the Ministry. After that, in the middle of a forest, Harry was trying to get Godric Gryffindor's Sword from a frozen lake when the Horcrux tried to drown him. Ron saved him and Harry told him that he should be the one to fight the Horcrux. When Ron tried to destroy it the Horcrux produced illusions of Harry and Hermione Granger, but when the illusions kissed themselves, Ron delivered a blow that destroyed the Horcrux.
Helga Hufflepuff's Cup
Hufflepuff's Cup was the fourth Horcrux to be destroyed. It was created from the murder of Hepzibah Smith (through poison). It was destroyed by Hermione Granger in the last book, and in the second part of its movie adaptation. It was chosen by Voldemort to be an Horcrux because it was from the great witch Helga Hufflepuff. Its destruction is just mentioned in the book, but its shown in the movie, where Hermione and Ron return to the Chamber of Secrets and use a Basilisk fang to destroy it.
Rowena Ravenclaw's Diadem
Ravenclaw's Diadem was the fifth Horcrux to be destroyed. It was created from the murder of an Albanian peasant. It was destroyed by Harry in the last movie, and accidentally by Vincent Crabbe in the last book. It was chosen by Voldemort to be an Horcrux because it was from the great witch Rowena Ravenclaw. In the movie, after a duel with the Slytherin students, Gregory Goyle, casts an fiendfyre spell and after running from it, Harry stabs the Diadem with a Basilisk fang and Ron kicks it into the fire. In the book, the spell is cast by Crabbe and accidentally destroys the Diadem.
Nagini was Voldemort's pet snake and the seventh and last Horcrux to be destroyed. It was created from the murder of Bertha Jorkins. It was destroyed by Neville Longbottom in the last movie/book. It was chosen by Voldemort to be an Horcrux because it was the symbol of his power and his ability to speak to snakes, which was a rare ability. In the middle of the battle in Hogwarts, Nagini was pursuing Ron and Hermione who were uselessly casting spells at her, when Neville suddenly appeared and cut the snake's head off.
Accidentally when he tried to kill Harry, Voldemort imprisoned a part of his soul into him, turning him into an Horcrux. The Horcrux in Harry was the sixth Horcrux to be destroyed. It was destroyed in the last movie/book, by Voldemort himself, though he did not know what he was doing. Voldemort cast a death curse in Harry, causing him to "die". When Harry went to something that looked like a limbo, where he found something that looked like a blooded baby version of Voldemort and Dumbledore's spirit. Since Harry had more than one soul, he could choose to die or to return; either way, the Horcrux's fate was sealed. During that point, Harry learned that Voldemort's soul was damaged so much that he was beyond anyone's help when he found a part of it in Limbo.
Powers and Abilities
Harry has the abilities of a common wizard, he also shares Voldemort's power to speak to snakes and has a mind connection with him. Nagini has a great resistance to spells (as shown in her fight against Harry and Hermione, and then with Ron and Hermione), a very powerful and corrosive poison (which is shown in the fifth book in Arthur Weasley's wound made by her) and also a uncommon intelligence level. Being only objects, the other Horcruxes show the ability to project illusions and invade weak minds, in some cases, controlling or disabling them as an act of defense.
If they stay in emotional contact with a person, Horcruxes can also drain such person's life force using them to revive the Horcrux's owner. If Harry didn't destroy Tom Riddle's Diary, the Horcrux would have drain Ginny Weasley of her life force, allowing Voldemort to return. According to author J.K. Rowling, not only would Voldemort return, but he would have come back even stronger.