Attack on Arthur Weasley

The attack on Arthur Weasley occurred a couple of days before the Christmas holidays in 1995, while he was on duty guarding the prophecy regarding Lord Voldemort and Harry Potter. He was bitten by Lord Voldemort's snake, Nagini. He was grievously injured and sent to St Mungo's Hospital for Magical Maladies and Injuries.

The Prophecy
"The one with the power to vanquish the Dark Lord approaches…Born to those who have thrice defied him, born as the seventh month dies…And the Dark Lord will mark him as equal, but he will have power the Dark Lord knows not…And either must die at the hand of the other for neither can live while the other survives…The one with the power to vanquish the Dark Lord will be born as the seventh month dies..."

- Sybill Trelawney

In 1980, Sybill Trelawney made a prediction regarding a boy born at the end of July who was destined defeat the Dark Lord; part of this prophecy was overheard by Severus Snape. Snape hastened to tell Lord Voldemort, who interpreted it as referring to Lily Potter's son. Voldemort pursued the Potters for a year, during which time they went into hiding with the use of the Fidelius Charm. When their Secret-Keeper, Peter Pettigrew, defected to the Death Eaters, he gave in to Voldemort's threats against his life and divulged the Potters' location. James and Lily Potter died defending their son, the latter directly sacrificing herself by refusing to move when Voldemort ordered her to "stand aside;" Lily's act of love afforded Harry a form of protection so powerful that it caused Voldemort's Killing Curse to rebound back on to himself. The fragment of Voldemort's Soul that resided in his body was driven out, kept alive by his Horcruxes but forced to exist in a weak, spectral form.

After the prophecy had been made, a record of its contents was kept in the fabled Hall of Prophecy in the Department of Mysteries at the Ministry of Magic.

The Return of Lord Voldemort
"Who put your name in the Goblet of Fire, under the name of a different school? I did. Who frightened off every person I thought might try to hurt you to prevent you from winning the tournament? I did. Who nudged Hagrid into showing you the dragons? I did. Who helped you see the only way you could beat the dragon? I did."

- Barty Crouch Jr. to Harry Potter

In 1994, thirteen years after Lord Voldemort's initial defeat, the Triwizard Tournament was held at Hogwarts School of Witchcraft and Wizardry. Bartemius Crouch Jr., disguised as Alastor "Mad-Eye" Moody through the use of Polyjuice Potion, made sure that Harry Potter survived all three tasks and successfully won the tournament, so that he would be sent to Voldemort after touching the Triwizard Cup, which had been turned into a Portkey.

Harry and Cedric Diggory, by consensus, grasped the cup simultaneously, and were both transported to the Little Hangleton graveyard, where Diggory was immediately killed by Peter Pettigrew. Harry was then bound to Tom Riddle Sr.'s grave, and watched as Pettigrew prepared a potion, using Harry's own blood to restore Voldemort, to true corporeal form.

With Harry's blood coursing through his veins, Voldemort was certain he had found a means of overcoming Lily Potter's Sacrificial protection, and discovered that he could indeed touch Harry without experiencing the excruciating pain he had in 1992. Seeking to prove that Harry had so far survived only on the basis of flukes and technicalities, rather than some inherent flaw in Voldemort's own magical knowledge or ability, he initiated a duel with Harry. His attempts at eliminating the threat Harry posed failed once again, as the twin cores of their wands caused the rare Priori Incantatem effect, and Harry was able to escape with Cedric Diggory's body and return to Hogwarts, alerting the world to Voldemort's return.

After failing on three separate occasions to eliminate the "Chosen One," Voldemort set plans in motion to acquire the prophecy record, determined to hear it for himself and in its entirety, to discover what the previously missing portion contained. His constant paranoia, and ego, may well have led him to believe that no one else would be capable of comprehending the complexities of the prophecy.

The Attack
While Arthur Weasley was guarding the door to the Department of Mysteries for the Order of the Phoenix, as the Order had anticipated that Voldemort would attempt to retrieve the prophecy and hear it in its entirety, Arthur fell asleep, and was attacked by Voldemort's snake, Nagini. Harry was able to view the events in his sleep through his connection with Voldemort, who was possessing Nagini at the time of the attack, and upon awaking, insisted that the vision had not been just been a dream. Professor Minerva McGonagall brought Harry and Ron Weasley to Headmaster Albus Dumbledore's office, where Dumbledore sent Professor Everard to his other portrait at the Ministry to sound the alarm, and Professor Phineas Nigellus Black to his other portrait at 12 Grimmauld Place to alert the Order. Dilys Derwent was likewise dispatched to her portrait at St Mungo's, to report to the headmaster when Arthur was admitted. Dumbledore then created a portkey, which he used to send Harry and the Weasley children to Grimmauld Place

Aftermath
Arthur was sent to St Mungo's Hospital for Magical Maladies and Injuries and was placed in the ward for creature-induced injuries, on the first floor. He was given a Blood-Replenishing Potion, as he continued to bleed profusely any time his bandages were removed, suggesting that Nagini's venom somehow prevented or delayed blood clotting. Trainee Healer Augustus Pye suggested using the Muggle remedy of "stitches" on his wounds, which failed to work when the stitches simply dissolved. Arthur eventually made a full recovery and returned to Grimmauld Place.

In the moment that Dumbledore finally looked Harry in the eyes for the first time all year, seconds before the portkey left for Grimmauld Place, Harry was overwhelmed by an urge to attack the Headmaster; this, along with the fact that he had viewed the attack through Nagini's eyes, made Harry fear that he was being possessed by Voldemort. The entire event prompted Dumbledore to begin Harry's Occlumency lessons with Snape.

Appearances

 * Harry Potter and the Order of the Phoenix
 * Harry Potter and the Order of the Phoenix (film)
 * LEGO Harry Potter: Years 5-7