Gygax's iconic spider demon-goddess, first appearing in the GDQ series of modules.
In real world religions, spider-deities are uncommon, and are often trickster gods, not evil chthonics. Japanese folklore has several demonic spider beings (Tsuichigumo and Joroogumo). Greek mythology contains the story of Arachne, a woman who was turned into a spider by Athena, and appears in a half-spider, half-woman form in Dante's Divine Comedy (the name Arachne would later appear in a novel of Gygax's). Fictional possibilities are from Tolkien's work (which include the spider monsters Ungoliant and Shelob), and Clark Ashton Smith's Atlach-Nacha, a spider god with a human face.
Unlike drow, the name Lolth does not appear to be borrowed from folklore, although the Welsh word lloches - 'lurking place, to hide inside caves' is a possible source.