Gellert Grindelwald

"Kill me, then! You will not win, you cannot win! That wand will never, ever be yours!"

- Grindelwald taunting Voldemort, shortly before his death

"I refuse to bow down any longer..."

- Grindelwald, disguised as Percival Graves

Gellert Grindelwald is a minor villain, yet a very important background character from the Harry Potter series of books and their movie adaptations ,but acts as the main antagonist of the 2016 film Fantastic Beasts and Where to Find Them. He is considered by many to have been one of the most powerful Dark Wizards in history, only second to Lord Voldemort.

He attempted to take over Europe during the Second World War, but was defeated by the protagonists' mentor Albus Dumbledore in 1945 and imprisoned until his death to the Dark Lord.

In Harry Potter and the Deathly Hallows - Part 1, the younger version of Grindelwald is portrayed by Jamie Campbell Bower, while the older version is portrayed by Michael Byrne. In the Fantastic Beasts film series, he is portayed by Johnny Depp and Colin Farrell who were also portrayed Sweeny Todd, Bullseye and Bobby Pellitt.

Background
Gellert Grindelwald was schooled at Durmstrang Institute, a reputed school of wizardcraft in Central Europe, rather infamous for its tolerance towards the Dark Arts, but was expelled at sixteen years old due to his unhealthy experiments. He then took up a friendship with Albus Dumbledore (who wound up falling in love with him) when he lived in Godric's Hollow for a summer with his great-aunt, Bathilda Bagshot, following his expulsion.

The two made plans to find the Deathly Hallows and create a world in which Muggles would be subservient to wizards and witches. This partnership fell apart after the two were involved in a three-way duel with Aberforth Dumbledore that resulted in Ariana Dumbledore's death. Grindelwald left Britain and soon stole the Elder Wand, an extremely powerful wand which vastly magnified its wielder's might, building an army and rising to power in continental Europe. During his reign of terror, he murdered many wizards and Muggles.

Fantastic Beasts and Where To Find Them
The extent of Grindelwald's success in his revolutionary endeavours is unclear, but his activities gathered international attention and were reported in American wizarding newspapers.[11] In 1926, MACUSA president Seraphina Picquery grew concerned about a threat to the Statute of Secrecy and believed that Grindelwald might be responsible, something which she would have considered an "act of war", showing how seriously Grindelwald's reputation was percieved in America.

Unbeknownst to Picquery, Grindelwald had already infiltrated MACUSA by assuming the identity of her right-hand man Percival Graves. Grindelwald believed the mysterious attacks occurring New York City to be the work of a powerful Obscurial, which he felt would be a great asset for his plans of world domination. Using his disguise as Graves, Grindelwald came into regular contact with Credence Barebone, whom he believed to be connected to the Obscurial due to a vision he received. Believing Credence was an orphaned Squib, Grindelwald manipulated him into helping him find the Obscurial with the promise of protecting him from his abusive adoptive mother and teaching him magic. During this time, Grindelwald (as Graves) arrested Newton Scamander, whose escaped pets were believed by MACUSA to be the cause of the Obscurial's attacks. During his interrogation, Grindelwald discovered the Obscurius within Newt's suitcase, and in an effort to hide his tracks, had him and Porpentina Goldstein sentenced to death. Afterwards, he approached Credence after Mary Lou Barebone was killed by the Obscurial and had him track down his adoptive sister Modesty Barebone, believing her to be the source of the Obscurial. Once they found Modesty, Grindelwald cruelly rejected Credence, as he had no further use of him. This angered Credence, who then revealed that he was the Obscurial, much to Grindelwald's surprise. Grindelwald attempted to convince Credence that he had nothing to fear any more and to join his ranks, but this further angered Credence who began rampaging through the city. After the Obscurial's death at the hands of the Aurors, Grindelwald was apprehended by Newt, who then revealed his real identity. Despite his rather easy arrest, Grindelwald was able to escape his captors and fled the United States, eventually ending up in France.

Massing his forces
Grindelwald eventually established a prison, Nurmengard, to serve as a form of containment for his enemies, apparently sufficiently impregnable that he was later imprisoned in it, inaccessible to his former supporters and breached only by Voldemort. In what few accounts of Grindelwald's revolution exist, his great power as a wizard is mentioned often, but there is less mention of his crimes. One murder is noted, that of Viktor Krum's grandfather, and presumably there were others. He was also noted to be capable of darkness from a young age: he and Dumbledore discussed quite openly the idea of ruling Muggles as benevolent overlords, and suggestions were made to the effect that his experiments were too dark even for Durmstrang, a school with a dark reputation to begin with, leading to his expulsion.

Battle Against Dumbledore
In 1945, at the height of his power, his former friend Dumbledore confronted him due to the cries of the public and defeated him in what became known as a legendary duel. Grindelwald was subsequently imprisoned in his own prison, Nurmengard, on 1945, where he remained for the rest of his life.

Death
When Voldemort was in search of the Elder Wand, he traveled to Nurmengard and questioned Grindelwald, who taunted Voldemort by his true name and refused to give him any information about, which Harry believed was because Grindelwald did not want Dumbledore's tomb desecrated as Grindelwald may have still considered Dumbledore as a friend and may have been remorseful about his actions. Angered by Grindelwald mocking him, Voldemort killed Grindelwald with the Killing Curse.

Trivia

 * In the film adaptation of the final book, Grindelwald does not redeem himself as he does in the book, as he tells Voldemort where to find the Elder Wand. Though his death is not made obvious, there is a flash of light as Voldemort Disapparates that could have been the Killing Curse.
 * In Fantastic Beasts, Grindelwald is somewhat similar to Barty Crouch Jr., the main antagonist from Harry Potter and the Goblet of Fire. Both impersonate a highly respected Auror, only to have their identity revealed at the film's climax.
 * In the same film, Grindelwald proved to be more dangerous than New Salem Philanthropic Society and had had bigger plan than its leader Mary Lou Barebone, as he had bigger plan than anyone else and Nes Salem Philanthropic Society yet to become the major threat.
 * WatchMojo.com listed Gellert Grindelwald as among their honorable mentions on their Top 10 "Most Evil Harry Potter Characters" list.