|Dark Force Defence League|
Battle the Dark Arts.
Ministry of Magic (possibly)
Gilderoy Lockhart claimed to be an honourary member of this organisation, though given his inability to use magic competently, his membership could probably be credited to the heroic deeds published in his books (all of which were accounts of feats accomplished by far more able wizards, whose memories Lockhart modified after stealing their stories). How he managed to function inside it was unknown, but he lost his membership when his Memory Charm backfired and erased most of his own memories, which led him to be hospitalised in St Mungo's Hospital for Magical Maladies and Injuries for life.
Prior to the start of the Third Task of the Triwizard Tournament, Rita Skeeter published an article "Harry Potter: Disturbed and Dangerous" in which it was revealed that Harry possessed the gift of parseltongue. In the article, she quoted an anonymous member of the Dark Force Defence League, who stated that "Personally, I would be highly suspicious of anybody who could converse with snakes, as serpents are often used in the worst kinds of Dark Magic, and are historically associated with evildoers."
- Gilderoy Lockhart (former member)