Shelob is the giant spider who attacks Frodo in Cirith Ungol in J.R.R. Tolkien’s The Lord of the Rings.
Shelob lives in a tunnel above the pass of Cirith Ungol, near Mordor. Gollum guides Frodo and Sam toward her lair, hoping that the spider will kill them and leave the One Ring available for him to recover. Shelob stings Frodo, but Sam drives her away with Sting and the Phial of Galadriel.
Tolkien describes Shelob as a descendant of Ungoliant, a much older and more powerful spider-like being from the First Age. Ungoliant helps Morgoth destroy the Two Trees of Valinor before fleeing into darkness. The two characters are therefore related in the legendarium but are not the same creature. Mirkwood’s spiders are another separate group, encountered by Bilbo and the Dwarves in The Hobbit.