A very influential work on philosophy and political theory, The Republic is a Socratic dialogue, written by Plato around 380 BC, concerning justice, the order and character of the just city-state, and the just man. The book made popular the term 'philosopher king', an ideal ruler who loves knowledge, has and loves intelligence, is reliable, and willing to live a simple life. The philosopher king  would be ideal ruelrs of Plato's utopian city Kallipolis.