Question: What organization founded by Albus Dumbledore did Snape become a double agent for in the series "Harry Potter"?
Sentence (from "Severus Snape"): 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.
Relevant evidence: No