Shelob is the great spider defeated by Samwise Gamgee in J.R.R. Tolkien’s The Lord of the Rings.
Shelob lives in a pass near Cirith Ungol, above the route Frodo and Sam take toward Mordor. She attacks Frodo, who is paralyzed by her venom, but Sam uses the sword Sting and the Phial of Galadriel to drive her away.
Shelob is descended from Ungoliant, a much older and more powerful spider-like being from Tolkien’s mythology. That connection gives Shelob a place in the wider history of Middle-earth, although she is not presented as one of the giant spiders of Mirkwood.
A common mix-up is to answer Ungoliant because she is the most famous ancient spider in the mythology. Ungoliant belongs chiefly to the First Age, while Shelob appears during the events of The Lord of the Rings.