Over time, the Hallows fell into legend. Very few knew they truly existed and because of this, very few tried to search for them. Out of this sprung a legend which said that whoever united the Hallows by possessing all three at the same time would become the Master of Death.
Harry is not immortal because he owns all three of the Deathly Hallows and becomes master of death; he is master of death because he accepts his mortality. He owes his survival to this acceptation and any other explanation goes against the moral of the entire story.
At different points, Dumbledore possessed all three Deathly Hallows. He won the Elder Wand from Grindelwald, had the Invisibility Cloak in his possession when James Potter died, and wore the Resurrection Stone as it sat in Marvolo Gaunt's ring.
Albus Dumbledore and Harry Potter are the only known people to have held each of the three Hallows, although neither possessed all three simultaneously (the closest was Harry being the Elder Wand's master, though not in physical possession of it, while having both the Stone and the Cloak in his physical possession).
The Dark Lord — aka Voldemort — created seven Horcruxes in an attempt to sustain immortality. But, as you may have heard, Voldemort's plan ultimately failed. Harry Potter and co. found and destroyed all of his Horcruxes.
So when Ron said three, it wasn't a mistake. He meant there were three more horcruxes to destroy before being able to destroy the fourth and final piece which was in fact Voldemort himself.
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.
Draco had several reasons for lying to Bellatrix, including the fact that he was never a bad person. Moreover, he no longer found working for the Dark Lord appealing and hated how Voldemort treated his family. He did not intend to harm anyone and believed Harry was the only person capable of defeating Voldemort.
Author JK Rowling announced Albus Dumbledore was gay in 2007. It's known that he and Grindelwald were in a romantic relationship but it had never been explored in the previous Harry Potter films. Fantastic Beasts 3 might address the depth of their relationship.
The three Deathly Hallows – the Invisibility Cloak, the Resurrection Stone and the Elder Wand – have tempted many a wizard over the years.
Even if he had known about them, Dumbledore speculated that he wouldn't have cared: Voldemort chose Horcruxes, not Hallows, always wanting to work alone rather than rely on anything or anyone else. The exception to this was the third Hallow – the Elder Wand.
Where did James Potter get the invisibility cloak from? James got it from his own father. The Invisibility Cloak was a Potter family heirloom, handed down from father to son for centuries. It was made by Ignotus Peverell, a distant ancestor of James.
Harry revealed that Draco was still very much alive, and she lied to her master in order to get closer to him. Narcissa may have concealed the truth from Voldemort to save her son, but she inadvertently helped Harry to victory in doing so.
Cruciatus Curse ('Crucio')
Harry tried to use this spell himself. The first time was against Bellatrix after she had killed Sirius.
Bellatrix Lestrange Killed her own cousin, Sirius Black: She killed Sirius (who was her cousin) during the battle at the Department of Mysteries. She was remorseless and was cackling in glee after she had murdered Sirius.
The most likely reason why Lord Voldemort's nose disappeared and he devolved into such an evil-looking creature is that as he dabbled deeper into the Dark Arts, his appearance gradually became as distorted as what remained of his twisted soul.
Though Harry encountered many opportunities that deemed Avada Kedavra necessary, it remains as one of the Unforgivable Curses Harry Potter never cast. For one, he viewed the spell as an immoral practice commonly used by users of the Dark Arts.
Voldemort wanted to humiliate Dumbledore, not kill him directly. Plus the story wouldn't allow it, the book would have been over so quickly. Voldemort was a dark lord that could have also been killed MANY times with the killing curse, but what story would there be if that happened?
According to The Leaky Cauldron, when a fan asked if Hermione made sure that her parents could remember her again, Rowling said, "she brought them home straight away." This is good news, as it's awful to imagine Hermione's parents never remembering who she is or ever seeing her again.
Scabbers was actually, as we know, Peter Pettigrew, an unregistered animagus hiding out as the Weasley's pet rat. No matter how hard he focussed his intention on turning the rat yellow, or even if he'd said the words rattus colovaria (erm, we did our best) the spell would never have worked because the rat wasn't a rat.
Quirrell tried to put up feeble resistance on occasion, but Voldemort was far too strong for him. Quirrell is, in effect, turned into a temporary Horcrux by Voldemort. He is greatly depleted by the physical strain of fighting the far stronger, evil soul inside him.
In 1998, Fred participated in the Battle of Hogwarts, defending the castle's passageways with his twin. While fighting alongside his brother, Percy, he was killed in an explosion possibly caused by Death Eater Augustus Rookwood.
The Emerald Potion, also known as the Drink of Despair, is a mysterious potion which induces fear, delirium, and extreme thirst. According to Dumbledore, the potion cannot be penetrated by hand, vanished, parted, scooped up, siphoned away, transfigured, charmed, or otherwise made to change its nature in any way.
While this was never definitively answered, I would suggest that Dumbledore was only certain that Harry was a Horcrux at the end of the Second Year. He would only have this confirmed for him during Harry's Fourth Year, however.