Plato, in the Republic, undertakes to show what justice is and why it is in each persons best interest to be just. The political discussion is undertaken to aid the ethical one. The ideal state, according to Plato, comprises three social classes: rulers, guardians (or soldiers), and producers (farmers and craftsmen). The rulers, who are philosophers, pursue the good of the entire state on the basis of their knowledge of the form of the Good and the form of the Just.
Plato ancient Greek philosopher, student of Socrates, teacher of Aristotle is best known as the author of philosophical works of unparalleled influence. His works also contain discussions in aesthetics, political philosophy, theology, cosmology, epistemology, and the philosophy of language. In metaphysics, Plato envisioned a systematic, rational treatment of the forms and their interrelations. His school brought in a wide range of efforts that today would be called mathematical or scientific. Plato introduced the idea that our mistakes are due to their not engaging properly with a class of entities which are Justice, Beauty, and Equality.
As a young man, Plato was a member of the circle around Socrates. There are works of Plato which are commonly referred to as Socratic as they represent the sort of thing the historical Socrates was doing.