Socrates: Socrates is the main character in The Republic. Plato uses his teacher to advocate his own ideas about how society should be governed. Socrates was one of the most influential Greek philosophers, and is credited with inventing the Socratic dialogue. Perhaps his greatest accomplishment was the education of Plato, who eventually surpassed his instructor in intellect.

Cephalus and Polemarchus: This father and son combination offer their home to Socrates toward the beginning of The Republic. Though they express their own ideas about justice, they are of little importance to the theme of Plato's work.

Glaucon and Adeimantus: These are other men involved in the early discussion in Cephalus' house. They, likewise, offer certain viewpoints, which Socrates uses to expand his own vision of human society.

Thrasymachus: This man also helps Socrates define justice in the opening scene when he asserts that it is better to live unjustly.