The Order of the Phoenix was a secret society founded by Albus Dumbledore to oppose Lord Voldemort and his Death Eaters. The original Order was created in 1970, after Voldemort returned to England from abroad and started his campaign to take over the Ministry of Magic and persecute Muggle-borns. The Order worked with the Ministry to oppose the Dark Lord and his followers, and played a crucial role in the First Wizarding War. Victory came in 1981 at the cost of many of their members.
The Order disbanded, but was reconvened in 1995 after Harry Potter informed Dumbledore of Lord Voldemort's return. The Ministry refused to admit that the Dark Lord had returned, thus the Order alone worked to protect Harry Potter and the prophecy concerning him and Voldemort in the Department of Mysteries. After a battle occurred there in 1996 between the Order and the Death Eaters, the Ministry admitted the truth. However, the next year would see the Order losing their leader and the Ministry being conquered by Voldemort. The Order remained an underground resistance, trying to protect Muggles and broadcast the truth during the worst days of the Second Wizarding War. They answered the call to arms by Dumbledore's Army on 2 May, 1998, fighting Voldemort and his Death Eaters for the final time at Hogwarts School of Witchcraft and Wizardry. The Battle of Hogwarts ended with Voldemort's death and a decisive victory for the Order and their allies.