U is for Ungoliant

Dude on the right? Sauron's daddy.

One of the creepiest of Tolkien's forces of Evil, Ungoliant was a spirit who took the form of a massive Spider. Her children (like Shelob, the nasty big Spider in Lord of The Rings) roamed the dark places of the land, making nests at devouring all who come into their lairs.

One of the stranger things about Ungoliant is that she did not get the usual eighteen-page backstory that most of Tolkien's creations received - she simply is, and in a world as detailed and recorded as Middle Earth, that's pretty creepy. It's obvious, however, she's old - as in "older than the world" old. Best guess, she's a spirit of hunger, famine, and despair, created during (or maybe a by-product of) the creation of Middle Earth, taking those qualities and clothing herelf in the form of the first Spider. There are also a few hints that she was spawned of The Void - the massive nothing outside of Middle Earth. So she might be a Ginat Alien Spider.

She's so representative of Hunger, in fact, that she spawned her own Young, just to eat them. Only a few escaped and spawned themselves, creating legions of demi-god spiders roaming the dark bits of Middle Earth.

Oh shit.

And her Hunger was her demise - she ran out of things to eat in her darkened lair, so she ate herself completely.

The reason I mention her here is because I love the idea of a whole race who physically stem from such an evil God/Spirit/Whatever. How much cooler would Trolls be, for instance, if they were the outbred, lessened descendants of some crazed God of Life, never truly able to die, simply driven on by his rage. Or maybe something more monstrous, like the Grell - giant flying brains with octopoid bodies. Maybe they were chunks of some God, or his descendants, cursed to take mortal form for some slight against a more powerful God.

It makes for an interesting bit of worldbuilding, and also a handy reason for them being Always Chaotic Evil - they're born that way and that's that.

Mind you, I am of the opinion that all spiders are Always Chaotic Evil, so don't mind my bias.