Question: The fictional character in J. K. Rowling's "Harry Potter" series Severus Snape becomes a double-agent on behalf of this secret organisation to fight Voldemort and his followers known as what?
Sentence (from "Severus Snape"): Snape becomes a double-agent on behalf of Albus Dumbledore and the Order of the Phoenix, and protects Harry throughout the series.
Relevant evidence: Yes