Shelob was a child of Ungoliant, which was an ancient hideous female being, believed to be the personification of Kúma, the Primeval Night, the Void itself, who took the form of an enormous ghastly Spider.
History
Shelob was a huge creature in spider form, apparently the spawn of Ungoliant and some lesser spider of Arda. She dwelt high in the mountains of Mordor, where she had established her lair before Sauron claimed Mordor as his own. Shelob spent her early days there feeding off elves and men, but as elves and men became scarce in the area, she fed upon orcs. Sauron would sometimes send her captured prisoners for whom he had no further use and amuse himself watching how she played with her prey. Even though they did not communicate, Sauron and Shelob understood each other. To Sauron Shelob was somewhat like a pet, and despite not being whatsoever a servant of his, she served as a secure guardian of the pass of Cirith Ungol to prevent any intruders from entering the Dark Land.
Torech Ungol, Shelob’s Lair, was along the path that Samwise Gamgee and Frodo Baggins took while seeking Orodruin, commonly known as Mount Doom. Their guide, Gollum (whom the orcs of the Tower of Cirith Ungol call “Shelob’s Sneak”), had reached some sort of understanding with her, and he led the hobbits directly into her trap.
While put off by the Phial of Galadriel in the tunnels, she intercepted them again outside and attacked Frodo, stinging him into a death-like coma. Sam managed to defeat her by letting her impale herself upon Sting when she tried to crush him under her massive body. Wounded, she fled to her lair and was never seen again.
Thinking Frodo dead, Sam took the One Ring from him and left his body behind, but discovered by listening to a party of Orcs that Shelob’s venom was not intended to kill its victims but only to render them unconscious and keep their meat fresh.
Etymology
The name Shelob is derived from “lob”, an archaic English word for spider. A variation, “cob” is the derivation of the word “cobweb”. The first element, “she”, simply implies the spider’s gender.
