Shelob appeared in the third installment of the Lord of the Rings trilogy, The Return of the King.
Shelob was one of the countless brood of Ungoliant, an ancient monster in arachnid form, created, possibly, by the perversions of Morgoth. Shelob was the greatest of Ungoliant’s spawn, many times larger than even the largest of Mirkwood’s spiders. Shelob took up residence in the Ephel Duath, near Cirith Ungol in the passes above Minas Morgul. For thousands of years she resided in this mountainous region, making a labyrinth of webs within a network of caves to better entrap her would-be prey. She captured Frodo Baggins and incapacitated him and was fought off by Sam. She is also very similar to Aragog from Harry Potter.