Wendigo

A cannibalistic Native American spirit which can either transform into a human or who can possess a person, particularly if that person has eaten human flesh. Thus cannibalism was strongly discouraged among people who had the Wendigo in their mythology, even as a last resort to avoid starvation.

They were described as being so thin that the skin stretched across their bones but at the same time as being gluttonous, hardly being able to kill and eat enough humans to satisfy themselves.

Interestingly there is a phenomenon known as Wendigo psychosis where subjects kill and eat people, even though there is other food available. The person believes they have been possessed by the Wendigo spirit. Perhaps they have..