Slytherin's Locket

Salazar Slytherin's Locket was an heirloom of the Slytherin family, owned originally by Salazar Slytherin. It was a heavy gold locket with Sytherin's mark (a serpentine "S"). The locket was passed down the Gaunt family line to Tom Riddle's mother, Merope Gaunt. Merope sold the locket to Borgin and Burkes when she was pregnant with Tom and desperate for money, and it was later bought by Hepzibah Smith. Tom murdered Hepzibah and stole the locket to use as a Horcrux.

Powers
Before becoming a Horcrux, the locket was described by Hepzibah Smith as having "all kinds of powers", though she failed to elaborate. It also appears that one must be able to speak Parseltongue in order to open the locket's golden doors.

History
The locket was a creation and once the personal property of Salazar Slytherin, the celebrated Founder of Slytherin House at Hogwarts School of Witchcraft and Wizardry. It appears that when Slytherin created the locket, he enchanted it so that only a Parselmouth, like himself, could open the locket's golden doors. It is described as a heavy golden locket with an ornate, serpentine "S" made of glittering green stones, presumably emeralds (as the eyes of the snakes on the door to the Chamber of Secrets had emeralds for eyes). Slytherin took the locket with him when he quarreled with the other Founders (especially Godric Gryffindor) about admissions to Hogwarts and left the school.

After Slytherin's death, the locket was passed down his family line, eventually ending up in the hands of the Gaunt family. The locket was one of the family's two final remaining family heirlooms (along with Gaunt's Ring) at the time of Marvolo Gaunt and his children, Morfin Gaunt and Merope Gaunt. Contradictory to his obsession with the two heirlooms, Marvolo permitted Merope (whom he horribly mistreated) to wear the locket around her neck (almost strangling her to death once while trying to show it to Ministry of Magic official Bob Ogden. After her brother and father were imprisoned in Azkaban for assaulting Muggles and Ministry officials, Merope made her move for Tom Riddle Sr. and ran away to London with him, subsequently becoming pregnant with his child.  After she released Riddle from her enchantment, he immediately deserted her and returned to Little Hangleton, leaving Merope to mourn her loss.  As she wandered the streets of London heavy with child, she was in desperate need of money.  She sold her only valuable, the locket, to Caractus Burke for only ten galleons, either not realizing that the locket was a priceless artifact or having simply ceased to care. Not long afterward, she was again destitute and stumbled to a Muggle orphanage on New Year's Eve night, giving birth to her son Tom Marvolo Riddle and dying shortly thereafter.

Many years later, Tom Marvolo Riddle graduated from Hogwarts and took a job at Borgin and Burkes, his job being to "persuade" people to part with their magical valuables (a job he proved to be extremely efficient at performing). One day, Tom visited the elderly witch Hepzibah Smith and charmed her with flowers and compliments. Due to Riddle's charming influence, Hepzibah decided to show Tom her most prized possessions. First, she showed Riddle Helga Hufflepuff's Cup, an artifact that had been created by her own ancestor, the Founder of Hufflepuff House. Next, she showed him something she even noted herself that Tom was sure to like even more: the locket. She revealed that both objects had considerable powers she had not fully tested and recounted the locket's next line of history. Hepzibah told Riddle that she had paid a heavy price to Caractus Burke to obtain the locket and that Burke had previously bought it from "a ragged-looking woman" (Merope) and paid her a mere pittance for it, indicating that she thought Merope had most likely stolen the locket. By this time, Riddle had already committed the murders of his paternal family and knew of his lineage to Slytherin, and thus he knew that the "ragged-looking woman" Hepzibah was referring to was his own mother. Upon hearing this story, his eyes turned their trademark red for a brief moment as he tightly clutched the locket's chain. Hepzibah seemed to have noticed the dark look in Riddle's eyes, but paid it no mind as he handed the locket back over to her and successfully hid any sign of his thoughts as always. Three days later, Hepzibah was found dead and her elderly house-elf, Hokey, admitted to poisoning Hepzibah's cocoa. In reality, however, Riddle had returned to visit Hepzibah again and poisoned Hepzibah himself. He then incapacitated Hokey and implanted a false memory into her mind making her actually believe herself to be the perpetrator. This was a mirror to Riddle's earlier murder of the Riddle family in Little Hangleton, where Morfin Gaunt's memory was modified as was Hokey's to divert blame away from the real murderer and resulted in the theft of a valuable artifact (the artifact being Gaunt's Ring in that case). Hepzibah's family later discovered the cup and the locket were both missing. Riddle disappeared shortly after Hepzibah's death, taking the cup and the locket with him, and was not heard of again for a decade.

For many years after this, Riddle kept the locket and the cup with him, eventually using Hepzibah's murder to make the cup a Horcrux and his murder of a Muggle tramp to turn the locket into one. The cup ended up in Bellatrix Lestrange's vault at her master's request. The locket, however, was hidden by Riddle himself. After turning the locket into a Horcrux, he returned to a cave he had visited as a child (where he tortured two of his fellow orphans Denish Bishop and Amy Benson). It was inside this cave that Riddle decided to store his ancestor's locket, where it was guarded by many enchantments and obstacles, the first of which was a door that could only be opened with a blood sacrifice. The second obstacle was an Infei-infested lake, in the middle of which was a small island where the Horcrux resided. The third obstacle was to find an invisible boat that would transport only one adult wizard to the island. The fourth obstacle guarding the locket was a basin filled with a mysterious green potion that could not be vanished, transfigured or otherwise made to change its properties. The only way to get rid of the potion and thus empty the basin and get to the locket was to drink it. Drinking this potion caused the drinker's insides to burn unbearably and caused them to see some of their worst fears as though in a bad dream. If the drinker had any strength left, they would be forced to drink water from the lake (as the potion was enchanted to render the drinker unable to drink any other water but the lake's own), and this would cause an army of Inferi to rise out of the water and attempt to kill the drinker. Riddle used the Black family house-elf Kreacher to test the locket's defenses. When he had seen the cave's effectiveness in action, he left Kreacher to die on the island in the middle of the dark lake. However, he miscalculated the fact that house-elves have different magic from that of wizards, and thus he was able to apparate out of the cave before the Inferi could drown him. Regulus Arcturus Black, one of Voldemort's Death Eaters, learned of these events from Kreacher and turned against his master due to his mistreatment and attempted murder of the house-elf. He forced Kreacher to take him back to the cave to obtain the locket, knowing of its nature as a Horcrux due to Voldemort's boasting of immortality previously. Regulus crossed the lake with Kreacher and drank the potion, telling Kreacher to switch the true locket with a fake one he had been given previously and to take it home and destroy it. He had ordered Kreacher to sail away without him afterward, and Kreacher, with the locket in hand, watched in horror as Regulus was drug beneath the lake by the Inferi as he crossed the lake and escaped back to the Black family home, [12 Grimmauld Place]].

Kreacher kept the locket safe for many years to come, trying desperately to destroy the locket to no avail. He deduced that the locket had to be opened in order to be destroyed (a theory later proven correct). He placed it in a glass case in the drawing room and left it undisturbed for many years until the Order of the Phoenix began to use the house as headquarters. The Order undertook a massive cleaning of the house, and the locket was thrown onto the rubbish pile to be thrown away. Kreacher stole the locket back however and took it to his cupboard along with some other Black family heirlooms that were headed for the trash. Mundungus Fletcher then combed the house and stripped it of its valuables after the death of Sirius Black, and stole the locket from Kreacher's cupboard. He then took it to Diagon Alley where he began to sell his wares, before being caught by Dolores Umbridge. Umbridge eyed the locket, took a fancy to it, and agreed to let Fletcher off for not having a license to sell things in exchange for the locket.

Some time later, Harry Potter journeyed with Albus Dumbledore to the Horcrux Cave, and they retrieved the fake locket Regulus and Kreacher had left there. Harry deduced that the R.A.B. from a note inside the fake locket was in fact Regulus, and together with Ron Weasley and Hermione Granger they questioned Kreacher about the locket. Kreacher brought Mundungus back to Grimmauld Place under Harry's orders, and they discovered the locket's fate. After extensive monitorization of the Ministry of Magic, Harry and his friends infiltrated the Ministry and took back the locket from Umbridge. For months, they were forced to merely keep the locket safe until they found a way to open it and destroy it. They took to wearing it, where it began to probe their minds, particularly Ron's. After finding the sword of Godric Gryffindor in the forest of Dean at the bottom of a frozen pool, Harry dived down after the sword, which had the power to destroy Horcruxes. The locket around his neck however tried to strangle him rather than allow him to acquire the sword. Ron returned in time to rescue Harry however, and ripped the locket from Harry's neck. After the two of them had recovered and Ron had obtained the sword, Harry spoke the word "open" in Parseltongue and opened the locket. It then began to create apparitions of Harry and Hermione that began to taunt Ron with his fear that Hermione and Harry loved each other romantically and that Ron would always be second-best in everything. It then attempted to possess Ron, until he broke through its influence and brought Gryffindor's sword down upon the locket, shattering its windows and deactivating it as one of Riddle's Horcruxes.

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"To the Dark Lord I know I will be dead long before you read this but I want you to know that it was I who discovered your secret. I have stolen the real Horcrux and intend to destroy it as soon as I can. I face death in the hope that when you meet your match you will be mortal once more. &mdash;R.A.B."

- A note found inside the fake locket.

In the spring of 1997, Albus Dumbledore and Harry Potter traveled to a remote cave on an island in a lake in an attempt to find the locket. After crossing an Inferius-infested lake, Dumbledore was forced to drink a sinister potion in order to get to the locket at the bottom of a large basin. It was later discovered that the locket in the basin was, in fact, a fake.

In Harry Potter and the Deathly Hallows, R.A.B. is revealed to be Regulus Black, and the true locket is hanging around the neck of Dolores Umbridge. Umbridge took it from Mundungus Fletcher in Diagon Alley, after Mundungus had already looted it from Black's home at Number twelve, Grimmauld Place. Hermione Granger takes it from around Dolores' neck after she, Harry, and Ron drink Polyjuice Potion and sneak into the Ministry of Magic. The locket is ultimately destroyed by Ron with Godric Gryffindor's sword.