Severus Snape becomes a double-agent in the secret organization founded by whom?
Albus Dumbledore
Title: Potions in Harry Potter
Passage: 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.
Title: Order of the Phoenix (fictional organisation)
Passage: 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".
Title: Severus Snape
Passage: 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.
Severus Snape Order of the Phoenix (fictional organisation)