Nagini was Lord Voldemort's final Horcrux Nagini was not only the last Horcrux to be killed, but also the last Horcrux to be created. In an interview, J.K. Rowling revealed that it was the murder of Bertha Jorkins that made Nagini a Horcrux.
When Jo Rowling was asked on the Bloomsbury webcast who died to make Voldemort's seven Horcruxes, she answered: The diary ” Moaning Myrtle. The cup ” Hepzibah Smith, the previous owner. The locket ” a Muggle tramp.
In short, no one knows exactly how Nagini ends up as Voldemort's closest ally. Evidently, something happened between the time of her joining Newt and the events of Harry Potter that pushed her to the dark side. She might even have met Voldemort while still human, and he was Tom Riddle.
However, Nagini gives him some advantages. By placing a piece of his soul in Nagini, Voldemort enables her to do his bidding in a way an ordinary snake would not. He can communicate with her and control her remotely, for instance. She is more perfectly his agent than even the most loyal Death Eater.
During the final battle of Hogwarts, Neville pulls the sword of Godric Gryffindor from the Sorting Hat and beheads Nagini, destroying the last Horcrux. This allows Harry to finally kill Voldemort after the latter's killing curse poetically backfires when Harry uses a disarming spell on him.
Lord Voldemort callously fed Muggle Studies teacher Charity Burbage to Nagini after performing the Killing Curse.
While most fans agree that Harry is the unrefuted Chosen One, the final Deathly Hallows film (in particular) sways heavily toward highlighting a heroic Neville, revitalizing the debate regarding which boy is better suited for the iconic title. "The one with the power to vanquish the Dark Lord approaches ...
When Harry and Hermione are on the first floor of Bathilda's house, Nagini (inside the corpse of Bathilda) tells Harry to "Come!" from the next room in Parseltongue. In reaction, Hermione jumps and clutches Harry's arm, and the two of them obey the command.
It wasn't just inanimate objects that could become Horcruxes. Lord Voldemort's beloved snake companion, Nagini, was also transformed into one, and Dumbledore seemed to know it, ominously predicting that a day would come where Voldemort would 'fear for his snake'.
The second film in the series, written by Harry Potter architect, J.K. Rowling, revealed in a trailer that fans had been on the right trail. Nagini, it turns out, was actually a Maledictus—a witch with a blood curse that turns her permanently into a beast (in her case, a giant snake).
Nonetheless, despite her initially benevolent nature, Nagini's blood curse eventually turned her into a snake permanently. Though it is unknown if she became evil as a result of that, or was turned evil as a result of Voldemort turning her into a Horcrux. As a snake, Nagini was completely loyal to Lord Voldemort.
Voldemort had a special relationship with Nagini, as she was his pet and one of his Horcruxes. According to Dumbledore, Voldemort had strong feelings for Nagini that he had not for anyone else; she was the one living thing that he had ever cared about.
Unless one or the other has a significantly smaller role in the films than we are led to believe, Dumbledore and Nagini will get to know each other. From the very little we see of Nagini, it looks like she's at least potentially on the same side as Dumbledore.
So when Ron said three, it wasn't a mistake. He meant there were three more horcruxes to destroy before being able to destroy the fourth and final piece which was in fact Voldemort himself.
Voldemort intentionally made six Horcruxes, but when he used Avada Kedavra on Harry, he unintentionally created a seventh Horcrux. Instead of dying, Lily's love for Harry created a counter 'curse' known as Sacrificial Protection and saved Harry.
Quirrell tried to put up feeble resistance on occasion, but Voldemort was far too strong for him. Quirrell is, in effect, turned into a temporary Horcrux by Voldemort. He is greatly depleted by the physical strain of fighting the far stronger, evil soul inside him.
This means that the killing curse (if I'm correct) has the power to destroy horcruxes. But when Ron and Hermione are about to die by Nagini, Ron casts the killing curse as a last resort and it simply rebounds off Nagini as it was nothing.
Nagini the Snake
Nagini was the last horcrux to be destroyed and also the last to be made. It was created when Peter Pettigrew bumped into Ministry of Magic employee Bertha Jorkins in Albania while Voldemort was still weak.
Harry Potter and the Deathly Hallows
In this book, Rowling reveals that Bellatrix is the guardian of Helga Hufflepuff's cup (though she is unaware that it is a Horcrux), which Voldemort has entrusted the Lestranges to keep in their Gringotts vault.
Erroneously believing Snape is the master of the Elder Wand and that Snape's death will make him the master of the Wand, Voldemort kills Snape by having his pet snake Nagini bite him through ...
In the belief that the Elder Wand will grant its allegiance only to one who has slain its previous owner, Lord Voldemort has his pet snake, Nagini, kill Severus Snape.
He was afraid that the Elder Wand, recognizing his true owner, wouldn't work as intended, or worse, backfire on him. Giving Nagini the order to kill, indirectly would have led him to win the Wand's allegiance as per him, without any side-effects.
However, the prophecy went on to say that Voldemort would mark the child as his equal, choosing the boy that he believed would be the most dangerous to him. Dumbledore believes Voldemort chose Harry because Harry was a half-blood, just like Voldemort.
In the end, both were essential to Voldemort's downfall, fulfilling the possibility that both Harry and Neville were, in fact, the Chosen One. While Harry delivered the final blow to destroy Voldemort, Neville destroyed the final Horcrux which allowed Harry to end Voldemort.
Thus, both boys eventually played their part in the prophecy: Neville rendered Voldemort mortal by destroying his last Horcrux which allowed Harry to inflict the final defeating blow upon Voldemort.