A Dementor is A dark amortal non-being creature which feeds on the happiness of humans, often thought to be one of the most foul dark creatures to inhabit the earth. Most commonly repeled with the Patronus Charm.
The Dementors are generally tied to one location, Azkaban, after the death of the one who built the fortress, the Dark Wizard Ekrizdis, the Dementors remained. The Ministry of Magic became aware of the Dementor infestation and decided to let the colony remain of the island, worried of what repercussions would come from attempting to clear them out. In 1718, Damocles Rowle became the Minister for Magic, and insisted on using the island as a prison, and the Dementors as guards, claiming doing so would not only save time and expense, but also countless lives, as the Dementors would not go searching for victims if they were given prisoners to feast upon. The Dementors were also used in extreme cases to give the Dementor’s Kiss, which removed the soul of a person while leaving them alive. The Dementors were also used to guard other locations in rare cases, most notably in 1993 after the escape of (wrongly) convicted “mass murderer” Sirius Black. The Dementors remained guards until 1996, when they abandoned their posts at Azkaban to join He-Who-Must-Not-Be-Named, as He offered the Dementors more victims and the ability to go where they pleased. After the Second Wizarding War, the newly elected Minister for Magic, Kingsley Shacklebolt, dissolved the Dementors guarding Azkaban. Information on the Dementors post-1998 is non-existent.
From the Latin verb dēmentō, meaning to make mad or crazy.