Dementor

One of the most terrifying creatures in the wizarding world, Dementors were wraithlike creatures that fed on human happiness and generated terrible feelings of despair within any person in close proximity. In the worst case scenario, a Dementor's Kiss would allow the Dementor to consume a human's soul, leaving them in a vegetative state. Although they were used as guards for the prison, Azkaban, Dementors were not known to permanently inhabit any other location. The only way to protect against Dementors was with the Patronus Charm and consuming chocolate would also alleviate some of the side effects of their close presence. Harry Potter was particularly affected by the Dementors due to the murder of his parents, to which his teacher, Professor Lupin, assured him was "nothing to do with weakness", and that "the Dementors affect you worse than the others because there are horrors in your past that the others don’t have."