According to Harry Potter canon, Nagini met Voldemort (Ralph Fiennes) sometime before 1994, possibly in Albania - which is where Voldemort murders Bertha Jorkins (after torturing her to find the whereabouts of Barty Crouch Jr.) in order to turn Nagini into a Horcrux.
Though it may later be revealed that the Dark Lord did indeed know that Nagini was a Maledictus, there's currently no indication that he (or anyone else) ever thought that she was anything other than a snake who was made into one of the Dark Lord's Horcruxes.
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).
So why is this a big deal? Because Nagini also happens to be the name of another iconic “Harry Potter” character — Lord Voldemort's magical, extremely murderous pet snake. Well, just in case there was any doubt, “Harry Potter” creator JK Rowling confirmed the two characters are one and the same.
Nagini, Voldemort's snake, then eats Professor Burbage's dead body. A story about her "resignation" from Hogwarts appears in the Prophet, but members of the Order of the Phoenix discount it, as they are unable to locate her anywhere after that. Burbage is later replaced as Muggle Studies teacher by Alecto Carrow.
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.
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'.
So it's possible that Nagini met Tom Riddle in his early years of rising to power but by the time she found him in Albania she had been cursed to become a snake entirely, and losing the ability to turn back into a human.
In Harry Potter, Nagini is one of Voldemort's closest followers, if not the closest. He turns her into a Horcrux, which attests to how close they are. Dumbledore eventually refers to Voldemort as being as fond of Nagini "as he could be of anything." However, the story of how they met is difficult to piece together.
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.
At the end of the last film, Grindelwald told Credence he was really Aurelius Dumbledore – the previously unheard of sibling of Albus. However, that wasn't entirely true. While Credence is a Dumbledore, he isn't the brother of Albus, Aberforth and Ariana. In fact, he's Aberforth's secret son!
Sorcerer's Stone - he speaks to the snake in the cage at the zoo. Chamber of Secrets - he tells Draco's conjured snake not to attack another student. Deathly Hollows - he speaks with Bathilda Bagshot (who is actually Nagini).
The only "emotion" Voldemort felt when Nagini died was fear because she was the second to last piece of his soul. If Nagini wasn't a horcrux, he wouldn't even have kept her around.
In the book, Neville kills Nagini, plain and simple. Neville is the unsung hero and he's the only one who ever attempts to kill Nagini because Harry tells him to. 2.
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.
Rowling previously revealed that Nagini is a Maledictus, which means she carries a blood curse that will doom her to transform permanently into a beast.
Once Voldemort became aware of the nature of Harry's quest to find and destroy the horcuxes he stopped using Nagini as a spy and infiltrator, trusting in his own “superior skills” to protect her from harm.
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.
"There was a rumour that Nagini was the snake Harry released from the zoo in Harry Potter and the Philosopher's Stone. This was proven false, as Nagini is some type of viper while the snake in the zoo was a boa constrictor. Furthermore, the snake was given a male voice in the film, while Nagini is female."
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.
Nagini was Lord Voldemort's final Horcrux
'There will come a time when Lord Voldemort will seem to fear for the life of his snake. ' Nagini was not only the last Horcrux to be killed, but also the last Horcrux to be created.
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.