A Naagloshii or Skinwalker is an immortal semidivine being with the ability to change shape. Harry has had personal dealings with both Shagnasty and Goodman Grey. It is first mentioned in Turn Coat.
Naagloshii used to be the semidivine messengers of the Navajo Holy Ones. are semidivine beings which can morph into the general shape of any animal. Instead of being an exact copy of a gorilla, for example, it will be gorilla shaped (longer arms than legs, tremendous strength, etc.) but still recognizably a demon. The term skinwalker is actually a more general term for naagloshii and those who were taught magic by them.(reference needed)
Naagloshii are shapeshifters. They are capable sorcerers that can use their own natural abilities. The more afraid you are, the more powerful they become. They have a horrific psychic stench and when seen with a wizard's sight can be devastating and debilitating. Although as far as we know that may be due to the Skinwalker in question being old and evil. Its difficult to say what kind of thing Harry would see if he were to use his sight on Goodman Grey for instance.
Naagloshii get stronger by eating the essence of practitioners—they eat magic and add their victim’s power to their own. Eating a wizard gives the naagloshii considerable power; therefore, a wizard's power attracts naagloshii, especially if the wizard is wounded. However, the longer the naagloshii stay away from their home tribal lands, the more power they lose.
Only a true shaman of the blood can drive naagloshii away by performing an enemy ghost way. 
The Naagloshii was virtually its own ley line, its own well of power, having an enormous amount of metaphysical mass. It disrupted even the dark flow of energy rising up through the tower on Demonreach. However, as it approached the cottage and the tower, the stone glowed with fox fire, revealing symbols in an unknown language that seemed to repel the creature away from the structures.
True skinwalkers are millennia old. They are typically only found in the American Southwest on tribal lands; it costs them power to stay away too long. The Ute and the Navajo and other southwestern tribes have the real stories about them.
The English word for semidivine doesn't really cover it. Most skinwalkers are just people—powerful, dangerous people. They're successors to the traditions and skills taught to avaricious mortals by the originals—the Naagloshii. Shagnasty is a real Naagloshii. Per some Navajo stories, the Naagloshii were originally messengers for the Holy People when they were first teaching humans the Blessing Way. Although they were supposed to leave the mortal world with the Holy People, a few didn't. Their selfishness corrupted the power the Holy People gave them. It can be assumed this happened pre-history, several millennia ago.
Morgan tells Harry of a previous encounter with a skinwalker, when Morgan led it onto a nuclear test range and stepped into the Nevernever, leaving the skinwalker to be destroyed by a nuclear weapon. 
In the seriesEdit
- Main article: Turn Coat
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- Main article: Cold Days
- Main article: Skin Game
In Skin Game, it was revealed that Goodman Grey is the son of a Naagloshii.
First introduced in the television series of The Dresden Files in the first episode, "Birds of a Feather", it can kill its victims and using its ability, skin them. Then it can take the form of the person. In the TV series it was destroyed with a magical energy amplifying and exploding device nicknamed the Doom Box.
- The Paranormal Pastor: The Navajo Skinwalker
- Navajo Skinwalker Legend | The Wichery Way
- Skin-walker - Wikipedia, the free encyclopedia
- What Is a Skin-Walker? - Wisegeek
- Skinwalkers - What Are They?
- What are Skinwalkers? - - Helium
- Shape Shifters in Native American Myths | eHow.com
- Skinwalker True Stories