WARNING: The following article contains spoilers for Fantastic Beasts: The Crimes of Grindelwald, in theaters now.
One of the most surprising elements announced as a part of Fantastic Beasts: The Crimes of Grindelwald is the involvement of Nagini. The massive snake from the Harry Potter series eventually becomes the most valuable of Voldemort’s’ Horcruxes, and is a consistent presence in his appearances throughout the latter books.
However, The Crimes of Grindelwald reveals that she wasn’t always just a snake. Instead, the massive serpent was actually a witch who was cursed with a heredity spell that would transform her into a snake. With that (absolutely bonkers) revelation, let’s look back at what we know about Nagini, and what it could mean for the character in the future Fantastic Beasts films.
Nagini was introduced in the fourth installment of the Harry Potter series, The Goblet of Fire. The snake proved incredibly protective of Voldemort, who at the time was in an incredibly weakened state. It’s unknown how he first came across the serpent, although there is no mention of the snake appearing during his first reign of terror before the events of the original series.
What we do know is that while Voldemort was in exile within Albania, he made a habit of using the assorted wild animals as allies and tools. Thanks to his ability to communicate with snakes, he connected with Nagini, who at the time was only in her snake form. After killing Ministry of Magic representative Bertha Jorkins, Voldemort used her death to turn Nagini into a Horcrux. Now containing a piece of his soul, Nagini became a constant companion of Voldemort.
Nagini proved a consistent force throughout the latter installments of the series. She came close to killing Arthur Weasley in Order of the Phoenix, and even managed to cost Harry his wand during The Deathly Hallows. Ultimately though, it was her status as a Horcrux that got her targeted by the heroes.
After all the other Horcruxes had been destroyed by the heroes, Nagini was slain by Neville Longbottom during the Battle of Hogwarts when he straight cut off her head with a sword.
According to JK Rowling, Nagini's status as a former witch who was turned into a snake had always been a part of the series. Nagini is, and apparently always has been a Maledictus, a person cursed to morph into an animal every night.
Eventually, she'd become unable to transform back into a human. During the events of The Crimes of Grindelwald, we learn that Nagini was actually a witch who had been forced into a traveling circus. During that time, she formed a bond with Credence Barebone and escaped alongside him.
But despite their connection, the questions surrounding his true identity haunted Credence and forced him to align with Grindelwald. Nagini doesn’t make the leap with him, and instead escapes the fires threatening to consume Paris alongside the other heroes.
It's not really elaborated why she doesn't choose to go with him, but it's worth noting that she ends up alongside the other dissenters. The film ends with her among the assembled heroes arriving at Hogwarts to discuss their next move with Dumbledore.