We meet an extremely large cast of characters during The Two Towers; some of the most important include:
Aragorn is the ranger (and so sometimes known as "Strider") who is also the heir to the throne of Gondor. He represents the best hopes of the Men of Middle-earth: the king who will return to reclaim his throne and restore order to the world. Aragorn must become comfortable as a decision-maker and a leader of others throughout The Two Towers.
Gandalf the White was formerly called "Gandalf the Grey," but he returns from his encounter with the Balrog as a more powerful wizard than before. Gandalf acts in many ways as the archetypal Wise Man throughout the remainder of The Lord of the Rings, carefully and knowingly guiding others through the dangers they face, and providing aid in desperate moments (as, for example, at the end of the siege of Helm's Deep).
Saruman is the wizard who has betrayed both the Council and the natural world by constructing a mechanistic fortress for himself at Isengard. He aspires, in vain, to power greater than that of the Dark Lord Sauron himself. His treachery is most clearly manifest in his voice, which he uses to speak false words of flattering comfort in an attempt to gain control over others.
Treebeard is the Ent-a shepherd of trees-who finds and befriends Merry and Pippin in the Forest of Fangorn. Treebeard represents the natural world. He is the Ent who "rouses" his fellow Ents to go to war against Saruman.
Theoden is the king of Rohan who, for many years, has been under the influence of Saruman. When we meet him, he is withered and decrepit; once Gandalf frees him from Saruman's influence, however, he is renewed. Theoden, as a "Fisher King"-like figure (see Summary and Analysis) thus represents his people, who emerge as renewed and (at least partially) victorious by the book's end.
Grima Wormtongue is the agent of the wizard Saruman who, through false council, has been poisoning the mind and heart of King Theoden-for example, turning him against his nephew Eomer. Wormtongue represents the futility of trusting in evil; by the end of Book III, he is a prisoner, along with his master, inside the tower of Orthanc, a prisoner the two of them have essentially created for themselves.
Faramir is a captain of Gondor. He is the brother of Boromir. Unlike his brother, he is wise enough not to try and force the Ring from Frodo. He knows that evil cannot be defeated through evil means.
Gollum is the hobbit-like creature who, long ago when called Smeagol, took the One Ring for his own. When he encounters Frodo and Sam as the hobbits are trying to enter Mordor, he becomes their guide with the intention of taking the Ring back. As Frodo continually extends mercy and pity to Gollum, however, Gollum seems to be on the verge of "redemption." Ultimately, though, Gollum cannot resist the Ring's lure. He arranges to betray Frodo and Sam to the giant spider Shelob-a resolve hardened when, as he sees matters, Frodo betrays him to Faramir's men.