Why it's Creepy
It's easy to feel uneasy while driving through the desolate desert roads of Arizona, especially at night, and particularly so when you hear a short burst of taps on your window while cruising at 60 mph and turn to see the shapeshifting, mutilated, half-human creature responsible for the high-speed interruption. Relax -- it's only trying to rip the flesh off your bones.
Legend
Ingrained in Arizona culture that when a Navajo woman was found brutally murdered in Flagstaff, the accused killer's defense in court was that the attack could have only been perpetrated by a Skinwalker. There's even a defined and well-documented portion of the state known as Skinwalker Ranch where you are most likely to see one of the creatures. Not that you'd actually want to.
Where is Came From
Like so many ancient American urban legends have roots in Native American folklore. While it's fairly hard to gather specific details -- as speaking of potentially sinister legends is seriously taboo in Navajo culture -- it's understood that what non-Navajos refer to as "skinwalkers" are witch doctors who have become an evil reflection of everything the Navajo nation values. Basically, they are men who've transformed into malevolent, murderous creatures that have no qualms using their spiritual powers to kill. Navajo medicine men are trained to learn both good and evil aspects of their power, and Skinwalkers are those who have turned to the Dark Side. It's all very Star Wars. And, frankly, still terrifying. -- Wil Fulton