Who defeats Shelob and saves Frodo?

Samwise Gamgee defeats Shelob and saves Frodo in The Lord of the Rings. After Shelob stings Frodo and leaves him apparently dead, Sam takes up the sword Sting and confronts the giant spider.

Sam uses the Phial of Galadriel to produce a powerful light that drives Shelob back. He then wounds her with Sting and the sword's blade, forcing the creature to retreat into her lair. Sam believes Frodo has died, but later learns that Orcs have taken Frodo to the Tower of Cirith Ungol.

This episode highlights Sam's courage and loyalty. He is not a warrior of the stature of Aragorn or Gandalf, yet he repeatedly acts when more powerful characters are absent. Sam also briefly carries the One Ring after taking it from Frodo's body.

In the book, Shelob is an ancient spider descended from Ungoliant. The film adaptation presents the same basic rescue, though some details of the confrontation and its aftermath are streamlined.