We've seen the villain in Fantastic Beasts before - here's everything you need to know about him for future movies

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Eddie Redmayne as Newt Scamander in "Fantastic Beasts and Where to Find Them."

Warning: There are spoilers ahead for "Fantastic Beasts and Where to Find Them."

"Fantastic Beasts and Where to Find Them" introduces fans to even more of J.K. Rowling's magical world of wizards, goblins, and otherworldly creatures in 1926 New York City. It also reintroduces one of the series' big villains.

We're not talking about Voldemort.

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Say hello to Grindelwald.

Near the end of the movie, Rowling, who wrote the script, reveals Johnny Depp is Gellert Grindelwald, a dark wizard who's been hiding in plain sight throughout the film. Grindelwald's plotting to start a war between wizards and No-Majs (the American term for non-magical beings).

And though Grindelwald eventually gets locked up by the end of "Fantastic Beasts," don't plan on him staying that way forever. He's shaping up to be the main antagonist in the four planned sequels.

While Depp's appearance as a bleach blonde magician may look foreign, the name Grindelwald should sound familiar to fans. Here's everything you should know about the dark wizard.

Grindelwald played a major part in the 'Harry Potter' series.

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Gellert Grindelwald in "Harry Potter and the Deathly Hallows: Part 1."

In the "Harry Potter" series, which takes place decades after "Fantastic Beasts," Grindelwald plays a big role and helped shape the course of world events in the 20th century. He was Albus Dumbledore's closest friend before turning into a Hitler-like figure who threw the magical world into turmoil in an attempt to dominate non-magical folk.

Grindelwald's first mention in the "Potter" series is inconspicuous. He's simply a name dropped on Albus Dumbledore's chocolate frog card in "Harry Potter and the Sorcerer's Stone": "Dumbledore is particularly famous for his defeat of the Dark wizard Grindelwald in 1945."

It's not until several books later in "Harry Potter and the Deathly Hallows" that he plays a bigger role. As Voldemort searches for The Elder Wand, which he believes will make him invincible, he traces its path to Grindelwald. Voldemort finds Grindelwald in Nurmengard, a prison Grindelwald built during his rise to power and was locked in after his fall. But he finds out that Grindelwald doesn't have the wand anymore, and kills him. (It turns out that Dumbledore obtained the wand after defeating Grindelwald in 1945.)

Harry Potter, Ron Weasley, and Hermione Granger learn about Grindelwald by accident.

At Bill and Fleur's wedding in "Deathly Hallows," Xenophilius Lovegood wears a necklace with the Deathly Hallows symbol on it. Viktor Krum, one of the wedding guests, instantly recognizes it as Grindelwald's sign and is upset. Krum attended Durmstrang, the Scandanavian magical school which Grindelwald attended. Grindelwald carved the symbol into a wall at Durmstrang when he was there, and it inspired - or horrified - some later pupils. Krum's grandfather, for his part, was killed by Grindelwald.

Later, Harry and the crew find out Grindelwald's sign is that of the Deathly Hallows - a trio of objects consisting of the Elder Wand, the Ressurection Stone, and the Cloak of Invisibility. If a wizard or witch were to possess all three Hallows, they were said to be the Master of Death.

Grindelwald used to be best friends with Dumbledore.

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Grindelwald was expelled from Durmstrang when he was 16 for "twisted experiments," according to the tabloid wizard journalist Rita Skeeter. After his expulsion in the late 19th century, he went to live with his great-aunt, the wizarding historian Bathilda Bagshot, in Godric's Hollow in England. (It's also the place where the Potters lived, decades later.)

Bagshot happened to be neighbors with the Dumbledore family. Albus Dumbledore and Gellert Grindelwald - both ambitious, talented, and idealistic teenage wizards - quickly became friends.

The two also expressed interest in the Hallows, but both teens had different reasons for seeking them out: Grindelwald wanted power, while Dumbledore thought the Ressurection Stone might bring back his dead parents.

Since Rowling announced that Dumbledore was gay, many have speculated that their mutual interest was also romantic.

The two planned a revolution.

"You cannot imagine how his ideas caught me, Harry, inflamed me," Dumbledore's portrait told Harry at the end of "Harry Potter and the Deathly Hallows." "Muggles forced into subservience. We wizards triumphant. Grindelwald and I, the glorious young leaders of the revolution."

According to Skeeter, who also wrote a not-entirely-accurate biography of Dumbledore shortly after his death, Dumbledore and Grindelwald planned to overturn the Statue of Secrecy, which keeps magical folk secret from non-magical folk, and establish a wizarding ruling class over Muggles.

They had different reasons. For Grindelwald, it was because he was an evil dude. For Dumbledore, it was a reaction to his sister Ariana being tormented by Muggles until she went mad.

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Harry Potter with the Elder Wand, one of the three Deathly Hallows, which he used to defeat Voldemort at the end of "Harry Potter and the Deathly Hallows."

The two coined the phrase Grindelwald used on his crusade decades later: "For the greater good."

Dumbledore and Grindelwald planned to leave Gordic's Hollow to pursue their ambition. Aberforth, Albus's brother, confronted him, saying he needed to take care of their sister Ariana. Grindelwald, enraged, attacked Aberforth, and Albus defended him. In the three-way duel, Ariana was killed.

After that, Dumbledore stayed home to take care of his brother. Meanwhile, Grindelwald fled from the duel and went on to find at least one of the Hallows on his own.

Dumbledore defeated Grindelwald in a legendary duel.

Grindelwald stole one of the Hallows, the Elder Wand, from the Eastern European wandmaker Mykew Gegorovitch.

From here, he dabbled more in the dark arts and rose to power. The details of his rise aren't clear, but we do know that he killed a lot of people (like Viktor Krum's grandfather) and established a prison, Nurmengard, for his enemies. He thought it was impregnable.

As Grindelwald became more infamous, Dumbledore faced him down. In 1945, in a duel for the ages, Dumbledore defeated him, leaving Grindelwald imprisoned in Nurmengard.

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Gellert Grindelwald in "Harry Potter and the Deathly Hallows: Part 1."

"In a list of Most Dangerous Dark Wizards of All Time, he would miss out on the top spot only because You-Know-Who arrived, a generation later, to steal his crown," Rita Skeeter wrote. Voldemort might also be the more powerful wizard. He's the only known person who ever broke into Nurmenberg.

In "Fantastic Beasts and Where to Find Them," Grindelwald tries to start a war.

Courtesy Warner Bros. Pictures

Grindelwald, secretly disguised as Graves.

Let's get some of the timeline straight.

"Fantastic Beasts and Where to Find Them" takes place in New York City in 1926. Dumbledore and Grindelwald's whirlwind summer at Godric's Hollow took place around 1899. And we know Dumbledore defeated Grindelwald in a duel in 1945.

So by the time "Fantastic Beasts" takes place, Grindelwald is in his 40s and his regime is on the rise. But he never became a significant part of British magical history, so his activities must have been mostly confined to Eastern and Central Europe.

At the end of "Fantastic Beasts," Percival Graves - the head auror at MACUSA and seemingly the second-most-powerful person in the American wizarding community - turns out to be Grindelwald in disguise.

Throughout the film, Graves enlists Credence Barebone, an orphan who appears to be a No-Maj, into helping him find an Obscurial. An Obscurial is a hard-to-control magical force that's unleashed when a wizard or witch doesn't express their magical powers.

There's a big showdown between Graves, Newt Scamander (the movie's main protagonist), and Barebone. Graves is brought to his knees, and Scamander performs a "revelio" charm to reveal him as Grindelwald.

Grindelwald is taken away. And while American wizards, unlike British ones, use the death penalty, Grindelwald makes it to future installments of the series. It's not clear yet how he'll make it out. Perhaps he has a few allies in MACUSA.

What will Grindelwald's role be in future "Fantastic Beasts" movies?

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David Yates, who's directing the "Fantastic Beasts" movies and who directed the final four "Harry Potter" ones, told my colleague Jason Guerrasio at Business Insider Grindelwald is going to be a major part of the next movie.

"Grindelwald is a major character and it's pretty big shoes to fill," Heyman said. "So you want someone who is charismatic, who is brave as an actor, who can stand up and is iconic. Johnny [Depp] is one of the few actors who has created several iconic characters and he's brave, he's a great artist, he's a great actor. So we went to Johnny and he said yes."

Heyman also confirmed that Dumbledore will be in the sequel. Casting is currently underway.

The next "Fantastic Beasts" movie is rumored to take place in Paris. Rowling herself said the series' five movies will span "19 years," meaning it will end in 1945, the same year Dumbledore dueled Grindelwald.

So the rest of the "Fantastic Beasts" movies will take place just as Grindelwald is rising to power, and possibly in Europe, and may end in a Dumbledore-Grindelwald showdown.

There's a lot of rich material to be explored in the next four (or possibly more, when it's all said and done) "Fantastic Beasts" movies. Hopefully, all of our questions will be answered.