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.