The pale skin, sunken eyes, thin (perhaps elongated) face, promient (though not necessarily razor-sharp) teeth are characteristic of a corpse. Humans are hard-wired to fear death. Think of the impact seeing a corpse would have had on early (hu)man. Even though death is everywhere, it is mysterious, something to be feared; and it is embodied by the physical characteristics of a cadaver. That, and vampires.

Changed my mind. Definetely Slenderman.

Ah, but the question is not what it is, but who it is. And what it is is a creature that lurks in our cities, yet also in our souls. But I assume you meant the persona of this frightning figure. That, I cannot tell. But what I can, is that the devil himself runs in fear when he sees it. War, famine, disease are nothing compred to him. And the very word of it's existance is so vile, that it can make one fall to illness. It's slumber is undisturbed-for the time being. But let us enjoy our peace, until it has awoken.

yeah so scarde

Aliens.

Another species that branched off from what became humans? I kind of like that idea.