In some Native American traditions (Navajo, Hopi, Mohawk...) the skin-walker or yeenaaldlooshii is a human who is able to shapeshift into various animal forms through witchcraft. Skin-walkers are generally considered frightening, evil, dangerous, and difficult to kill.
Yeenaeldooshi means literally "with it, he goes on all fours" in the Navajo language. The Mohawk Indian word "limikkin" is sometimes used to describe all skin-walkers.
Possibly the best documented skinwalker beliefs are those relating to the Navajo yee naaldlooshii (literally "with it, he goes on all fours" in the Navajo language). A yee naaldlooshii is one of several varieties of Navajo witch (specifically practitioner of the Witchery Way, as opposed to a user of curse-objects or a practitioner of Frenzy Way . Technically, the term refers to who is using his (rarely her) powers to travel in animal form. In some versions men or women who have attained the highest level of priesthood then commit the act of killing an immediate member of their family, and then have thus gained the evil powers that are associated with skinwalkers.
The Yeenaeldooshi are human beings who have gained supernatural power by breaking a cultural taboo. Specifically, a person is said to gain the power to become a yee naaldlooshii upon initiation into the Witchery Way. Both men and women can become Yeenaeldooshi and therefore possibly skinwalkers, but men are far more numerous. It is generally thought that only childless women can become witches.