"A Dementor is the after-image of a soul that has been killed with the Killing Curse," Hermione informs the reporters. "The burned after-image is severed in the violence of the curse. A fraction of a whole, the fragment of the soul is corrupted and becomes a tear on the fabric of reality, taking on physical form and becoming a Dementor. The Dementor seeks the memories and souls of humans in an effort to become whole once more."