In J.R.R. Tolkien’s fantasy novel The Lord of the Rings, the giant spider that attacks Frodo in Cirith Ungol is Shelob.
Shelob lives in a tunnel above the pass of Cirith Ungol, near Mordor. She is an ancient, monstrous spider who preys on creatures entering her lair. Gollum knows the tunnel and deliberately leads Frodo and Sam into it, hoping Shelob will kill them.
Shelob stings Frodo and paralyzes him, but Samwise Gamgee attacks her with Sting and the Phial of Galadriel. Sam also takes the One Ring briefly because he believes Frodo is dead. He later returns it when he learns Frodo survived.
Shelob is connected to Tolkien’s earlier mythology through Ungoliant, a primordial spider-like being. They are not the same character. Shelob is Ungoliant’s descendant, making her part of a much older lineage of darkness in Tolkien’s legendarium.