In J.R.R. Tolkien's Middle-Earth, Ungoliant was a great spidery demon, which worked with Melkor to break and corrupt the world, until they had a falling out over the disposition of a few Silmarils looted from Valinor. Ungoliant had several lesser offspring, the best known of which is probably Shelob; I have also heard that the giant spiders of Mirkwood are ultimately descended from Ungoliant as well (via Shelob). Those spiders, while large, were mere mites compared to their progenitors.
There is an amusing relationship between the Bored of the Rings characters, Sorehed and Schlob, which I think is really more a cognate of Melkor and Ungoliant's special relationship, than Sauron and Shelob's acquaintance.