According to Rowling's timeline,
Gellert Grindelwald
Gellert decided to steal the Elder Wand as part of his desire to obtain the Deathly Hallows and heard that Gregorovitch had it. The stunning spell Gellert cast on Gregorovitch was enough to make him the rightful owner of the wand.
Voldemort broke into the prison Nurmengard Castle, where Gellert Grindelwald was being held, and demanded to know the location of the Elder Wand. It was only during the confrontation in Grindelwald's cell that Voldemort learned Albus Dumbledore had claimed the wand in a duel decades back.
Gellert Grindelwald
When it appeared in Fantastic Beasts, the connection between the two stories may not have been immediately obvious to everyone. But Grindelwald has deep roots in the world of Harry Potter. He was one of the first wizards to look for tools for immortality that would eventually seduce Voldemort.
Their falling out came as a result of a three-way duel between them and Dumbledore's brother Aberforth that ended up killing his sister. As far as we knew, Dumbledore and Grindelwald didn't meet until 1945, when Dumbledore famously defeated Grindelwald in a duel and took the Elder Wand.
Dumbledore and Grindelwald took a blood oath to not fight each other. "Fantastic Beasts: The Crimes of Grindelwald," the second film in the series, reveals that as teenagers Dumbledore and Grindelwald undertook a blood pact that wouldn't allow them to move against each other.
It was said he felt remorse after a few years locked up, so he lied to Voldemort and knew enough occlumency to make Voldy believe him. As Dumbledore suggested, he lied so that Voldemort couldn't take over because he felt remorse, or as Harry suggested, he lied so Voldemort wouldn't open Dumbledore's tomb.
Credence Isn't Voldemort's Dad But He Could Be Snape's Grandpa.
Grindelwald was infatuated with Dumbledore. Both ingenious wizards with somewhat extreme ambitions, the two became inspired to find the Deathly Hallows and lead a revolution that would destroy the International Statute of Wizarding Secrecy, allowing wizards to rise as benign worldly overlords.
Albus was fascinated by Grindelwald's research on the Deathly Hallows and ideas of wizarding domination, and their friendship soon turned into a romantic relationship, in which Albus fell in love with Grindelwald.
Draco's refusal to reveal Harry's identity to Bellatrix was not because he liked him. It was because he believed that Harry was the only chance they had at defeating Voldemort. At first, Draco admired and revered Voldemort until he threatened his family's safety.
James inherited the cloak from his father, Fleamont Potter, who inherited it as a descendant of Iolanthe Peverell -- a granddaughter of Ignotus Peverell. The cloak passed down through generations of the family until it reached James and then Harry.
This nuance was lost on Lord Voldemort, who wrongly assumed Severus Snape held the Elder Wand because he was Dumbledore's killer, when in reality Draco had disarmed Dumbledore before Snape arrived on the scene, making Malfoy the wand's true new owner.
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.
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.
The name Gellert Grindelwald only appears in the archives later – in the first volume of the Harry Potter series where he is mentioned only briefly on the back of Albus Dumbledore's chocolate frog card.
In the new clip from Fantastic Beasts: The Secrets of Dumbledore, Albus Dumbledore can be seen admitting to being in love with Grindelwald.
Kendra Dumbledore (c. 1851 — early summer 1899) was a Muggle-born witch, the wife of Percival Dumbledore, and the mother of Albus, Aberforth and Ariana.
Given that the third film takes place in the early 1930s, we still have a little over a decade to go until the legendary duel in 1945 that netted Albus the Elder Wand (one of the Deathly Hallows) and saw Grindelwald trapped in his own castle until he was murdered by Voldemort years later.
Fantastic Beasts: The Secrets of Dumbledore confirmed that Credence Barebone/Aurelius Dumbledore (Ezra Miller) is the new Snape (Alan Rickman) through a very familiar line delivered by Aberforth Dumbledore (Richard Coyle). Fantastic Beasts 3 finally shed light on the Credence being Aurelius Dumbledore plot twist.
Credence captures the Qilin and returns to Grindelwald, not realising that two were born that night. Grindelwald later orders Credence to murder his uncle Albus Dumbledore in Berlin, claiming that the Dumbledores knowingly abandoned him.
Albus confirms to Creedence early on in the film that he is in fact a Dumbledore, quashing any rumor that Grindelwald had lied to the young boy in order to sway him to his movement. It is explained that Credence is the illegitimate son of Albus's younger brother, Aberforth (Richard Coyle).
Ollivander confesses that he told Voldemort to look to Gregorovitch for the wand, because Gregorovitch was rumored to possess it. However, though Ollivander knows about the history of the Elder Wand and its powers, he doesn't know about the Deathly Hallows or the wand's connection to the other artifacts.
Riddle ultimately changed his name, by way of an anagram, from "Tom Marvolo Riddle" to "I am Lord Voldemort", as a way of removing his own heritage and of exalting himself, and he killed the Riddle family, partly because they were Muggles, and partly because they abandoned him and his mother.
Gaunt's ring
After retrieving the ring Albus Dumbledore himself fell victim to a curse that, even when contained, would likely have killed him within the year. Once rendered defunct as a Horcrux, the stone was placed inside a Golden Snitch and left to Harry Potter in Dumbledore's will.