Lolth, the Spider Queen

Lolth was supposedly part of the first generation of Elves, one of the most powerful and intelligent. She grew to despise the Founding Pantheon, claiming they preferred mortals over her kind. There are dozens of stories where Lolth challenges a god to create something, or solve a problem, and they usually end with some kind of disaster. Other tales describe her travels and betrayals and magical discoveries across Tephra. For example, she boasted to another Elf that she could cross the Shield Mountains on foot before he flew over them using magic. Lolth cheated by transforming into a spider, riding in her rival's boot and leaping out ahead at the finish line - "I have been on your foot the whole time" she said. Spiders feature prominently in her legends, as beloved companions and useful tools. It seems Lolth liked their aesthetic.
One story from Dorend is called "Lolth's Last Trick" and describes how the Spider Queen lived among the humans of Kirohyne for years, becoming the people's champion against their wicked sovereign. Finally, she bested the tyrant with magic and put him into an endless sleep. But she did not deliver the new era of freedom that was promised. Instead, her devoted subjects followed her thoughtlessly into a tunnel and far beneath the earth, where they still reside today. Their dark cities are built according to Lolth's cruel whims, and they try to mimic her in form and in thought.

Of course it is impossible to prove that any Elf "took the snake's legs so that spiders could have more" and a half dozen more foolish fables. But Lolth's last trick does explain the fate of the original humans of Kirohyne. Their ruined city had been empty and "cursed" for as long as the folk of Dorend could recall, and modern residents soon suspected that their lich-mayor might be the mighty wizard king of that story. The Dread Lord gives no consistent answer when asked why he was asleep for thousands of years, claiming boredom on some occasions and imprisoning people who ask on other occasions. 
Dwarf explorers in the Underdark sometimes return with stories of "the drow". These seem to be an underground folk with pointed ears and spider imagery on their clothes, art, and even their bodies. Some are tattooed so densely with webs that they look purple or indigo blue. Drow are never seen on the surface, but perhaps they are the descendants of the stolen humans of Kirohyne.

There are plenty of Lolth stories, told by people across the world. Everyone knows at least one. Sometimes a local landmark is credited with being part of the story, like the high hill in the small village of Geraint where they say Lolth buried an orc king who could not be killed.

Lolth is always clever, but sometimes she is wicked and cruel, pitting other characters or even groups against each other. If Lolth is a villain, she does this for amusement, but Elves telling the same tale might say that the Spider Queen only reveals the existing weaknesses. In the example of the race across the Shield Mountains, she usually devours her rival at the end, which might be a moral like "don't trust a trickster" or simply just deserts, depending on the storyteller's point of view. Interestingly, Lolth is not a common bogeyman for parents to frighten their children into behaving - there are enough real Elves for those stories.