Tolkien published The Hobbit; or There and Back Again in 1937 as a children's book, in which he introduces Hobbits (and specifically the uncle of Frodo Baggins, Bilbo) and the wizard Gandalf—although Gandalf appears more like a kindly old man who dabbles in fireworks than as the powerful sorcerer he becomes in The Two Towers. In The Hobbit Tolkien also introduces the One Ring, although its true identity and power are not yet revealed. Gollum also appears in The Hobbit, as the possessor of the Ring prior to Bilbo's acquisition of it. In all, The Hobbit serves as something of a prelude to the events detailed in later works.

The Two Towers does not, actually, stand alone as a novel, but consists of parts three and four of a six-part novel, The Lord of the Rings, which is generally but not exclusively published in three...