The great spider in J.R.R. Tolkien’s The Two Towers is named Shelob.
Shelob lives in a tunnel near Cirith Ungol, the pass leading toward Mordor. Frodo Baggins and Samwise Gamgee encounter her while attempting to reach the land of Sauron. Gollum guides them toward her lair, intending that she kill them so he can recover the One Ring.
Shelob attacks Frodo and stings him, but Sam drives her away with Sting and the Phial of Galadriel. Believing Frodo dead, Sam temporarily takes the Ring. He later discovers that Frodo is alive but has been captured by Orcs at the Tower of Cirith Ungol, beginning a rescue sequence.
Shelob is not the same character as Ungoliant, the enormous primordial spider from Tolkien’s First Age mythology. The two are connected by Tolkien’s description of Shelob as one of Ungoliant’s descendants. “Mirkwood” is a forest, not a spider, while Lobelia Sackville-Baggins is a hobbit character.