Question: Severus Snape becomes a double-agent in the secret organization founded by whom?

full_context: Document 1: Severus Snape: Severus Snape is a fictional character in J. K. Rowling's "Harry Potter" series. An exceptionally skilful wizard, his coldly sarcastic and controlled exterior conceals deep emotions and anguish. A Professor at Hogwarts School of Witchcraft and Wizardry, Snape is hostile to the series' protagonist, Harry, the moment he sets foot in Snape's classroom; this hostility is rooted in Harry's resemblance to Harry's father James, who bullied and harassed Snape during their time at Hogwarts. Though philosophically attracted to the Dark Arts and Lord Voldemort's ideology of wizard supremacy, Snape's love for Muggle-born Lily Evans, Harry's mother, eventually compels him to defect from the Death Eaters. Snape becomes a double-agent on behalf of Albus Dumbledore and the Order of the Phoenix, and protects Harry throughout the series.
Document 2: Order of the Phoenix (fictional organisation): The Order of the Phoenix is a secret organisation in the "Harry Potter" series of fiction 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".
Document 3: Potions in Harry Potter: This is a list of potions used in the "Harry Potter" series. Many are mentioned in potions class at Hogwarts, which is taught by Severus Snape in books one to five and Horace Slughorn in books six and seven.
Document 4: Lord Voldemort: Lord Voldemort ( , or in the films; born Tom Marvolo Riddle) is a fictional character and the main antagonist in J. K. Rowling's series of "Harry Potter" novels. Voldemort first appeared in "Harry Potter and the Philosopher's Stone", which was released in 1997. Voldemort appears either in person or in flashbacks in each book and its film adaptation in the series, except the third, "Harry Potter and the Prisoner of Azkaban", where he is only mentioned.
Document 5: John Nettleship: John Lawrence Nettleship (1 August 1939 – 12 March 2011) was a British schoolteacher who taught chemistry at Wyedean School, Gloucestershire. His pupils there included Joanne Rowling, whose mother worked for some time as an assistant in his department. He has been stated to be a major inspiration for the character of Severus Snape in Rowling's "Harry Potter" series of fantasy books.
Document 6: Harry Potter and the Deathly Hallows: Harry Potter and the Deathly Hallows is the seventh and final novel of the "Harry Potter" series, written by British author J. K. Rowling. The book was released on 21 July 2007, ten years after publication of "Harry Potter and the Philosopher's Stone" (1997), by Bloomsbury Publishing in the United Kingdom, in the United States by Scholastic, and in Canada by Raincoast Books, ending the series that began in 1997 with the publication of "Harry Potter and the Philosopher's Stone". The novel chronicles the events directly following "Harry Potter and the Half-Blood Prince" (2005), and the final confrontation between the wizards Harry Potter and Lord Voldemort, as well as revealing the previously concealed back story of several main characters. The title of the book refers to three mythical objects featured in the story, collectively known as the "Deathly Hallows"—an unbeatable wand, a stone to bring the dead to life, and a cloak of invisibility.
Document 7: Harry Potter (character): Harry James Potter is the title character and protagonist of J. K. Rowling's "Harry Potter" series. The majority of the books' plot covers seven years in the life of the orphan Potter, who, on his eleventh birthday, learns he is a wizard. Thus, he attends Hogwarts School of Witchcraft and Wizardry to practise magic under the guidance of the kindly headmaster Albus Dumbledore and other school professors. Harry also discovers that he is already famous throughout the novel's magical community, and that his fate is tied with that of Lord Voldemort, the internationally feared Dark Wizard and murderer of his parents, Lily and James.
Document 8: Harry Potter and the Half-Blood Prince: Harry Potter and the Half-Blood Prince is the sixth and penultimate novel in the "Harry Potter" series, written by British author J. K. Rowling. Set during protagonist Harry Potter's sixth year at Hogwarts, the novel explores the past of Harry's nemesis, Lord Voldemort, and Harry's preparations for the final battle against Voldemort alongside his headmaster and mentor Albus Dumbledore.
Document 9: List of supporting Harry Potter characters: The following are supporting characters in the "Harry Potter" series written by J. K. Rowling. For members of the Order of the Phoenix, Dumbledore's Army, Hogwarts staff, Ministry of Magic, or for Death Eaters, see the respective articles.
Document 10: Albus Dumbledore: Professor Albus Percival Wulfric Brian Dumbledore is a fictional character in J. K. Rowling's "Harry Potter" series. For most of the series, he is the headmaster of the wizarding school Hogwarts. As part of his backstory, it is revealed that he is the founder and leader of the Order of the Phoenix, an organisation dedicated to fighting Lord Voldemort.
Document 11: Dumbledore's Army: Dumbledore's Army (or D.A. for short) is a fictional student organisation in J. K. Rowling's "Harry Potter" series that is founded by the main characters, Harry Potter, Ron Weasley and Hermione Granger, to stand up against the regime of Hogwarts High Inquisitor Dolores Umbridge, as well as to learn practical Defence Against the Dark Arts. It was founded in the fifth book, "Harry Potter and the Order of the Phoenix". Cho Chang conceives of the abbreviation "D.A." and Ginny Weasley conceives of the name "Dumbledore's Army".
Document 12: Harry Potter and the Order of the Phoenix (film): Harry Potter and the Order of the Phoenix is a 2007 British-American fantasy film directed by David Yates and distributed by Warner Bros. Pictures. It is based on the novel of the same name by J. K. Rowling. The film, which is the fifth instalment in the "Harry Potter" film series, was written by Michael Goldenberg (making this the only film in the series not to be scripted by Steve Kloves) and produced by David Heyman and David Barron. The story follows Harry Potter's fifth year at Hogwarts as the Ministry of Magic is in denial of Lord Voldemort's return.
Document 13: Ministry of Magic: The Ministry of Magic is the government of the Magical community of Britain in J. K. Rowling's "Harry Potter" series. First mentioned in "Harry Potter and the Philosopher's Stone," the Ministry makes its first proper appearance in "Harry Potter and the Order of the Phoenix". Throughout the books, it is generally depicted as either corrupt, incompetent, or both, with its high officials blind to actual events and dangers. It reaches a nadir of corruption before being effectively taken over by Lord Voldemort. At the end of the final book, following Voldemort's death, Kingsley Shacklebolt takes over the ministry, changing it for the better. By the time of "Harry Potter and the Cursed Child", Hermione Granger is the Minister for Magic.
Document 14: Severus Snape and the Marauders: Severus Snape and the Marauders is a 2016 American short film written by director Justin Zagri, based on "Harry Potter" characters by J. K. Rowling. It officially premiered on March 1, 2016 at the Youtube channel Broad Strokes Productions. The fan film caught the attention of BuzzFeed, "Entertainment Weekly", "Time",
Document 15: Hogwarts staff: The following fictional characters are staff members and denizens of Hogwarts in the "Harry Potter" books written by J. K. Rowling.
ground_truth: Albus Dumbledore