Naagloshii

A Skinwalker is a demon with the ability to change shape.

Description
A Skinwalker is a demon which can morph into the general shape of any animal. Instead of being an exact copy of a Gorilla, it will be gorilla shaped (longer arms than legs, tremendous strength, etc) but still recognizably a demon. Typically only found in the American Southwest on tribal lands.

In the series
Encountered in the novel Turn Coat, the skinwalker was thought to have followed Morgan because it was attracted to his power and his wounds (he was wounded escaping Wardens after being arrested for the murder of LaFortier). Harry first saw the skinwalker when he had the impression that he was being followed in the Blue Beetle and used his Sight to view through the roof unobtrusively. What he saw brought him to hysterics, and plagued his thoughts for the remainder of the novel. The skinwalker was eventually driven off by Injun Joe, who himself morphed into various animals perfectly suited to defeating whichever animal the skinwalker was imitating. Current whereabouts unknown.

In television
First introduced in the television series of The Dresden Files in the first episode, "Birds of a Feather", it can kill it's victims, and using it's ability, skin them. Then it wears the skin as a coat almost, and can trick people into believing they are the real person.