One of the first and most outlandish hunts on Supernatural takes place in the first season's second episode, "Wendigo." The episode is largely a transition piece that's meant to give the brothers time to cope with the sudden changes in their life. They've been reunited after a two-year separation, Sam's girlfriend Jessica was murdered, they're following the supposed trail left by their father and it's the first episode to show them on a full-fledged hunt. The pilot featured a hunt as well, but it was one they stumbled upon. Episode 2 features the Winchesters on the road officially hunting monsters, and for their first big hunt, they needed a unique bad. Enter the wendigo.
It's unfortunate that wendigos never got a second appearance on the show. Other monsters get multiple showings but the wendigo was a one-hit-wonder that, if not for some lucky flare guns, would have most definitely killed Sam and Dean. In the mythology of the show, a wendigo is a former human whose cannibalism transformed them into a literal monster. The act of cannibalization was usually forced upon them through extreme starvation.
According to John Winchester's handy journal, the term wendigo translates to "evil that devours." For whatever reason, the consumption of human flesh, which some cultures believe contains unique abilities when consumed, gave these people enhanced strength, speed, agility and extended life. Living in the woods, they become perfect hunters as they lured humans out of their campsites and into the night. They no longer look like people but take on a mutated appearance, and the only way to kill them is with fire.
Most of what is shown in Supernatural about the wendigo comes straight from the legends. Their giant goblin-like appearance is a result of extreme emaciation, with bodies that seem practically meatless, their bones can be viewed through their flesh, and in most depictions, they're completely hairless. In the stories, their bodies are described as being unclean from the ultimate betrayal that comes from eating their own species in an act that's poisoned their souls and minds, as if the evil bled through to the outside. The wendigo comes primarily from Native American folklore and translates to "the evil spirit that devours mankind," a longer version of what is said in Supernatural and is historically associated with cannibalism, murder and greed.
Overall, they are a representation of greed and almost anything that can be considered an extreme cultural taboo. If someone committed a sinful act, they were thought to be possessed by a wendigo. Similar to the series, a wendigo is created whenever a human must resort to cannibalism to survive. The legends began when aboriginal peoples and settlers started finding themselves stranded in the bitter northern winters for days, driven mad by hunger to the point where they were forced to eat their own dead in order to survive or even kill their hunting partners. Their true origin, however, can be traced back to the nations of the northeastern seaboard. The legend serves as a warning against selfishness with the hunger of the wendigo as a symbol of greed. No matter how much they consume, they'll never get full.
Many believe they are also a representation of colonialism as Indigenous peoples were forced to watch white strangers come on their land and take it all for themselves, wiping out any tribe that got in the way. They were greedy and insatiable. Nothing was enough. The wendigo, whose skin is often described as being ash pale, could very well be designed to resemble a hideous, mutated European. Also, most stories about them grew in popularity upon the arrival of the colonials.
While Supernatural did follow the bare bones of the legend, its version of the wendigo barely scratched the surface of the monster's rich history.