Shelob is an ancient, monstrous spider from J.R.R. Tolkien's books who serves as a major antagonist in The Lord of the Rings. She is a descendant of the primordial spider Ungoliant and lives in her lair, Torech Ungol, in the pass of Cirith Ungol leading into Mordor, where Gollum guides Frodo and Sam to her. Sam defeats her using the light of the Phial of Galadriel and Frodo's Elvish sword, Sting, though she is not killed. 

Shelob is the last of the great spiders. In her lair, she has a large network of tunnels filled with webs and the remains of her prey.​Shelob is described as having a terrifying presence, a paralysing stinger and powerful venom to keep her food fresh. Her hide is tough, but the light of Galadriel can harm her, which contains the light of a Silmaril, blinds her and forces her to retreat.

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Shelob was the most prominent. Her descendants include the smaller, but still large, Great Spiders of Mirkwood. The Mirkwood Spiders were the descendants of Shelob and are large, malevolent creatures that infest the forest of Mirkwood. Their size varies, with some being large enough to threaten Bilbo Baggins in The Hobbit.

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Ungoliant was the primordial, monstrous spider from which all other giant spiders are descended. She was a primordial spirit who allied with Melkor and grew in power by devouring the light of the Two Trees of Valinor. She is the mother of all giant spiders, but she is not directly in The Lord of the Rings. She fled to the Ered Gorgoroth and spawned her offspring before being driven away by the Balrogs of Angband. It is said she eventually devoured herself.