Wendigos who existed in areas where the Winter caused them to become isolated due to heavy snow and adverse conditions: in these harsh conditions it was believed that the practice of cannibalism was occasionally practiced and the Wendigo was believed to be the result of such actions. Often said to have been human the Wendigo became transformed via the act of cannibalism into an eternally hungry monster that had no real universal appearance: though a common depiction is of a deer-headed decomposing humanoid; or a large hairy humanoid with a heart of ice, the concept of the Wendigo was likely formed as a warning against cannibalism.
The Wendigo has become a popular monster in fiction and somewhat of a staple in horror/fantasy, like Sleepy Hollow and Supernatural, although depictions vary drastically from story to story (though the idea of a large hairy humanoid is still the most common one) - although the Wendigo itself is almost entirely mythological science has named a cultural phenomena the "Wendigo Psychosis".
This is a rare condition in which individuals start to crave human flesh even when other food is in supply and interactions with people suffering from this condition may also of contributed to the legend of the Wendigo. This mental illness is very similar to Cabin Fever and Isolationism, and sufferers often describe being influenced by an external malevolent force.