Defence/Defense Against the Dark Arts is a class at Hogwarts which teaches students about Dark Magic and how to deal with Dark Magic spells.

Dementors are Dark creatures that drain happiness, peace, and hope from humans. They sometimes have a hood, but always have a "robe" which is slightly shredded.

Albus Dumbledore was the Headmaster of Hogwarts from 1892 to 1997.