The Order of the Phoenix is an organisation in the Harry Potter series of books written by J. K. Rowling. Founded by Albus Dumbledore to fight Lord Voldemort and his followers, the Death Eaters, the Order lends its name to the fifth book of the series, Harry Potter and the Order of the Phoenix.
When the character of Tom Marvolo Riddle began to use the name of Lord Voldemort and declared war on the wizarding world, Dumbledore attempted to take control of the situation by founding the Order of the Phoenix. Several characters joined the organisation , seeking to prevent Voldemort from taking over the wizarding world and establishing a tyrannical new world order. During this period, before the events of the Harry Potter and the Philosopher's Stone, the Order sustained heavy losses, including the murders of the Prewetts, the Bones', and the McKinnons; and the permanent incapacitation of the Longbottoms at the hands of Bellatrix Lestrange and other Death Eaters.
Voldemort's first reign of terror ended after the murders of James and Lily Potter, and the unsuccessful attempt to murder Harry Potter at the beginning of the series. This severely diminished Voldemort's powers, and as a result the Order was temporarily disbanded.
However, towards the end of Harry Potter and the Goblet of Fire, Dumbledore called for its reinstitution due to Voldemort's return. Many of the original members returned; they were soon joined by recruits who effectively replaced those who had died in service during the first war. The Order established their headquarters at Number Twelve, Grimmauld Place, Sirius Black's family home, during the interval between the fourth and fifth books in the series. Dumbledore was the Secret-Keeper for the Order, meaning that only he could reveal the location of the Order’s headquarters to others. Dumbledore's death at the hands of Severus Snape in book six made the location vulnerable and it was abandoned in favour of The Burrow.
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