In the world of spirits, there are two who are very similar, and yet different, at the same time. The first is a Grim, which is most commonly known as a bad spirit or omen. The other is that of a church grim, which is quite the opposite of a regular grim. A church grim is a good spirit who watches over their church, in order to keep away the bad grims.
Appearance: As most spirits can, grims can take on many forms. Most commonly grims take on the appearance of a small black dog. Church grims are also said to take on the form of small misshapen dark skinned people.
Origin: The origin of the bad grim is unknown, but there are several stories as to the origin of the Church Grim. In Swedish tales, church grims are supposed to be the spirits of animals sacrificed by Christians at the building of a new church. In parts of Britain, early Christians often would bury a solid black dog under the ground of a new church, thus creating a church grim to keep away evil spirits, like those of an evil grim.
Influence on the Modern Day: The Grim does not have many influences on the modern day, but there is one in particular that shows up in modern literature. In the Harry Potter series, by J.K. Rowling, a Grim is a omen of death. Most commonly, this Grim is represented by a black dog, and Harry sees this dog several times throughout book three Harry Potter and the Prisoner of Azkaban.
Wikipedia.org: Church Grim