The giant spider that attacks Frodo in Cirith Ungol in Tolkien’s Middle-earth is Shelob.
Shelob lives in a tunnel near the pass of Cirith Ungol, above the route into Mordor. In The Lord of the Rings, Gollum leads Frodo and Sam toward her lair, hoping to recover the One Ring after Shelob kills Frodo. She bites Frodo and paralyzes him with her venom, but Sam attacks her with Sting and the Phial of Galadriel.
Shelob is described as a descendant of Ungoliant, the enormous spider-like being from Tolkien’s First Age mythology. The two are not the same character. Shelob’s name is an English formation meaning “female spider,” while Tolkien’s text connects her lineage to the older, more cosmic evil of Ungoliant. Sam’s rescue of Frodo allows the quest to continue into Mordor.