Wendigo

The Wiki Tells us:
Wendigo (other names; windigo, weendigo, waindigo, windago, witako, windiga etc.) is legend creature of Algonquian people (a Native American tribe). 
It is cannibalistic, another way to describe is that he eats human. Lore says it's a spiritual being and it can possess people.
And according to another description it was once human, in time it has began to eat human flesh and it has changed into the creature it is.

The Supernatural Show Tells us:
Moves too fast to see and hide well too. The claws, the way it can mimic a human's voice... it's damn near a perfect hunter, it's smarter than avarage human. This thing is a good hunter at day but unbelievable hunter at night.

Anasazi symbols for protection, wendigo can't cross over.

"Wendigo" is a Cree Indian word. It means "evil that devours". 
They are hundreds years old.
Each one was once a man.
Sometimes an Indian, or other times a frontiersman or a miner or a hunter.

How's a man turn into these things?
Well it's always the same story.
During some harsh winter, a guy finds himself starving, cut out from supplies or help.
He becomes a cannibal to survive, eating other members of his tribe or camp.

Cultures all over the World believe that eating human flesh gives a person certain abilities:
Strenght, speed, immortality...
If you eat enought of it, over years you become this, less than human thing. 
You are always hungry.
More than anyting, a wendigo knows how to last long winters without food.
It hibernates for years at a time.
When it's awake, it keeps it's victims alive, it stores them so it an feed whenever it wants.