Skinwalkers are beings of a spiritual nature within the Native American culture. A form of witchcraft supposedly makes the practitioner the ability to take on other animal's attributes. There are many explanations for the capacity of a skinwalker, such as a witch being able to take something of a person's and curse them or looking into the skinwalker's eyes can cause sickness or death. In Navajo culture, the skinwalker can even take over a person's mind and control them. There are legends that if you realize a skinwalker is coming for you, the curse can go back on the person who ordered it, or if you go and knock at his door and confront him, telling him you know he's the skinwalker, he will die.
According to University of Nevada-Las Vegas anthropologist Dan Benyshek, who specializes in the study of Native Americans of the Southwest, "Skinwalkers are purely evil in intent. I'm no expert on it, but the general view is that skinwalkers do all sorts of terrible things---they make people sick, they commit murders. They are graverobbers and necrophiliacs. They are greedy and evil people who must kill a sibling or other relative to be initiated as a skinwalker. They supposedly can turn into were-animals and can travel in supernatural ways."
As curses and unnatural practices go, there's nothing spookier than a combination of a physical monster along with evil intent and the ability to curse; the trinity of worst scenarios. This is not just a Native American culture belief. The Norse have berserkers (take on an uncontrollable fury) and bear shirts (take on the power and prowess of a bear), who can take on animal form.
Perhaps the most popular form of skinwalker in our culture is the werewolf. The werewolf legend includes the ability to transform at will or under the influence of a curse, from human to bipedal wolf. It's origins began in the medieval times when wolves were a very real threat to the humans in villages. Eventually, witchcraft trials included accusations of a practitioner turning himself/herself into a wolf. Many were referred to as wolf charmers.
There was a ranch in Northeast Utah called the "Skinwalker Ranch" that made for a very exciting and riveting book, "Hunt for the Skinwalker." This site had a lot of legends as a portal of sorts where skinwalker shape-shifting creatures, aliens, UFOs, poltergeist activity and even more occurred on that property. Whether there is any validity to the story's take on what happened there, it made for a most spine-tingling read.