The soul fragment contained within took the form of a young Tom Riddle. Riddle’s spirit could interact with anyone who wrote on its pages and show them visions of the past. However, this placed them in grave danger. After gaining their trust, Riddle could manipulate and possess his victim, eventually draining them of their life force. Considering the attacks on students once the Chamber of Secrets was opened and how close Voldemort came to restoration, the diary was an incredibly dangerous artefact.
This Horcrux proved immune to Hermione’s Revealer and the Aparecium spell, plus it survived activities that would disfigure an ordinary book, like being drenched with ink or flushed down a toilet. Perhaps the diary’s greatest defence was its discretion, as it was easily mistaken for a common, Muggle-made object.
The ring was hidden in the remains of the Gaunt family shack, and the defensive spells placed around it had to be overcome by a very powerful wizard. After retrieving the ring Albus Dumbledore himself fell victim to a curse that, even when contained, would likely have killed him within the year. Once rendered defunct as a Horcrux, the stone was placed inside a Golden Snitch and left to Harry Potter in Dumbledore’s will. Its magic was last used to recall Lily, James, Sirius and Lupin as Harry prepared to face death.
Voldemort himself never learned the significance of the stone.
Slytherin’s locket was kept in a cliffside cave protected with a burning potion, the need for a blood sacrifice and an army of Inferi lurking in the water. Voldemort even went to the trouble of using a house-elf to test the locket’s defences, but he failed to consider what might happen should the elf survive the ordeal.
The locket’s protection did not end at the cave. The Horcrux survived multiple attempts at destruction by Harry, Hermione, Ron and Kreacher. During its travels, the locket revealed another line of defence – the ability to feed into negative emotions and corrupt the wearer. This effect was strong enough to cause the loyal Ron Weasley to abandon his friends.
The locket’s toxic influence could account for more than we realise. Kreacher’s bitterness might possibly have been influenced by his long-term exposure to the locket. However, Dolores Umbridge, admittedly not the nicest person to begin with, didn’t seem to change all that much while wearing it.
Voldemort left the cup in the hands of his faithful Death Eater Bellatrix Lestrange. Bellatrix was more careful with her Horcrux than Malfoy and kept it locked away in her vault at Gringotts. The bank offered top security including the Thief’s Downfall, the Gemino and Flagrante Curses and, of course, a dragon. If it weren’t for Bellatrix’s temper and the rage she showed when she feared her vault had been compromised, this Horcrux might never have been uncovered.
Hufflepuff’s cup was said to possess magical properties before being made into a Horcrux, although Hepzibah never got around to testing them. It also changed shape – and size – quite considerably during development.
‘I did consider making Helga Hufflepuff's hallow a cauldron, but there was something slightly comical and incongruous about having such a large and heavy Horcrux; I wanted the objects Harry had to find to be smaller and more portable.’
The diadem had been stolen by Helena Ravenclaw and was so well hidden in the forests of Albania that it went undiscovered for centuries. Voldemort took the diadem to the Room of Requirement which, in hindsight, might not have been his greatest tactic. The diadem was destroyed, along with nearly everything else in the room, by Vincent Crabbe who unleashed the Fiendfyre curse.
Rowena Ravenclaw’s diadem was said to grant wisdom to the wearer. It is unknown if the headwear retained this property or, if like some other Horcruxes, it could damage minds using Dark Magic. It seemed to have no effect on the members of Dumbledore’s Army as they practised nearby; however, there was another person who frequented the Room of Requirement in isolation – Draco Malfoy.
Could the presence of a Horcrux have worsened his already fragile mental state?
The final Horcrux created by Voldemort was a vicious snake, reinforcing his connection to Salazar Slytherin.
With her terrifying appearance and sharp fangs, Nagini’s greatest form of defence was attack. While some Horcruxes gradually ate away at people’s minds, Nagini could quickly destroy and literally devour their bodies. She also proved extremely useful in other ways. Her venom was used to make a potion to sustain Voldemort, she acted as a sentry in the old Riddle house and she was used to lay a trap for Harry and Hermione at Godric’s Hollow.
Once Voldemort realised his other Horcruxes had been compromised, Nagini was encased in a protective magical sphere and ordered to stay close. Voldemort however became complacent when he believed he had killed Harry, giving Neville Longbottom a swing at the snake. The rest, as they say, is history.
Living Horcruxes can be a liability. But Nagini was not the only one...
Besides being a wizard, Harry Potter’s magical properties included speaking Parseltongue, having a link to Voldemort’s mind and also the blood protection left by his mother’s sacrifice. After learning of this powerful magic, Voldemort attempted to harness it for himself and took Harry’s blood to regenerate his own body. However, he failed to understand the nature of Lily’s protection.
For many years Voldemort had sought to create a Horcrux with links to Godric Gryffindor, but Harry ended up turning Gryffindor’s sword into a weapon capable of destroying the other Horcruxes.
Of all the mistakes Voldemort made, it was Harry who really proved his undoing.