When Harry wrestles Draco's “everyday” wand out of his hand at the Malfoy's mansion, he conquers Draco, and therefore the Elder Wand — hidden in Dumbledore's tomb at the time — transfers its allegiance to Harry. Rowling said her American editor suggested the moment when Harry conquers Draco should be more dramatic.
Draco was the owner of both wands at that time. Wizards can have more than one wand, especially if one of them is the Elder wand. The only reason Harry has the Elder wand is exactly because he won Draco's wand in the first place, and then all his wands would follow that wand in changing (or sharing) allegiances.
Harry was taken to the Malfoy Manor after his capture by the Snatchers. When Dobby came to rescue them, Harry used the expeliamus charm to take Malfoy's wand, in the process taking the allegiance of the Elder wand as well.
Harry returned Draco's wand, as he had no reason to keep it when he had repaired the holly wand. He would undoubtedly have returned it as a gesture of goodwill and healing after the defeat of Voldemort.
It was taken from him by Harry Potter in Malfoy Manor in 1998, which would have unforeseen and enormous consequences in Harry's final duel with Lord Voldemort.
Harry Potter's wand shot a stream of golden flames at Lord Voldemort of its own accord during the Battle of the Seven Potters. The spell was powerful enough to break Lucius Malfoy's wand.
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.
Draco Malfoy's mother Narcissa was cold, cunning and devoted to the Dark Lord. But she was also a mother, which meant she was willing to risk everything to make sure her son was safe. When Harry survived Voldemort's Killing Curse for the second time, Narcissa pretended he was dead so she could get to Draco.
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.
Actions have consequences – Draco learnt that the hard way. Harry would later risk his own life to save Draco from the Fiendfyre. Narcissa Malfoy would then lie to Voldemort – an extremely dangerous person to lie to – and spare Harry to hear that her son is alive.
“Dumbledore didn't want to lose his wand at that point and Draco disarmed him. So that meant that the wand gave Draco its allegiance, even though Draco never knew it, even though Draco never touched it. “From that moment on, that wand gave its allegiance to Draco, and it wouldn't work as well for anyone but Draco.”
During his final confrontation with Voldemort, Harry knew that he (Harry) was the Elder Wand's true master. He again cast Expelliarmus, ejecting the wand from Voldemort's hand into his own as the Killing Curse rebounded off his body, fatally striking Voldemort.
Specifically, Draco was jealous of Harry. It was easy to miss because Draco didn't often show his emotions, modelling himself on his cold, confident, calculating father, but J.K. Rowling has confirmed that a lot of his enmity towards Harry stemmed from envy.
Malfoy spots Harry and casts a Cruciatus curse; Harry, defending himself, using the Half-Blood Prince's Sectumsempra spell without knowing its effects. To his horror, it gashes Draco's face and chest, spilling his blood everywhere.
Voldemort hugged Draco as an improvisation and it wasn't planned. Even Tom Felton (Draco Malfoy) was caught unaware which increased the effect. In Harry Potter style, it was like a welcome for Draco, but as Voldemort had never known love, he didn't know how to hug him very well. Thats why they had the awkward hug.
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.
Her sacrifice gave Harry the power of love, a protection spell sealed with the blood spilled by her death.
This theory suggests that each time he created a new Horcrux, that specific Horcrux diminished a part of his soul. Thus, his nose began to sink in, eventually disappearing altogether. Due to his tampering with dark magic, his human appearance evolved into a more snake-like state.
Narcissa's greatest moment, however, was when she chose to betray Voldemort in Harry Potter and the Deathly Hallows. Not knowing whether Draco was alive or dead, Narcissa chose to lie to the Dark Lord rather than risk losing her son.
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.
When Voldemort has killed Harry Potter and Narcissa checks on Harry, she lies to Voldemort and tells him Harry is dead. She also wants to know how Draco is doing, but she could have asked Harry, then called out that Harry was actually alive after Harry answered her.
The Elder Wand, the most powerful wand ever created, is one of three objects that make up the Deathly Hallows, including the Cloak of Invisibility and the Resurrection Stone. The Elder Wand was 15 inches long, formed by Death himself, made of elder wood, and contained the center of the tail-hair of Thestral.
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.
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.