Both the narrator and the main philosopher of the Republic dialogue. Socrates, invited (and slightly taken hostage) to his home by Polemarchus while returning from a religious ceremony, conducts the greatest philosophical debate on the concept of justice in history throughout the night with the city's intellectuals, poets, and sophists. By refuting all claims with his sharp intellect, he saves philosophy from speculation and places it on a moral and ontological foundation (the Idea of the Good). By establishing the parallel between 'State' and 'Soul', he creates a balance between philosophy (wisdom), military power (courage), and production (temperance), defining justice as each part doing its own job perfectly. The concept of the philosopher-king and the Allegory of the Cave are the zenith of his journey of reason and enlightenment.
Although from the lower classes of Athens, he became a central figure in the city's intellectual circles because of his philosophical genius. The fact that he would be executed by the Athenian state for corrupting the youth and not believing in the gods looms in the reader's mind as the bitter backstory to his theses that 'there is no place for a philosopher in a corrupt state' and 'if the state does not make the philosopher king, it prepares its own disaster.'
Although not described in much physical detail within the text, ancient accounts and allusions depict him as an elderly sage in modest attire, bald and snub-nosed, focusing on mental perfection rather than bodily pleasures.
Glaukon
His favorite thinking partner; he encourages him by generating ideas.
Adeimantos
The valuable guide who allows him to shift the discussion to sociology and education through practical problems.
Thrasymakhos
A cynical sophist whose power show he does not take seriously and whose ideas he masterfully dismantles.