Plato (c.427-347 BC) was one of the shapers of the whole intellectual tradition of the West. He was disgusted by the corruption of Athenian political life, and the execution of his teacher Socrates. He sought cures for the ills of society in philosophy, and became convinced that those ills would not cease until philosophers became rulers, or rulers philosophers.
Trevor J. Saunders has translated many volumes of Plato for the Penguin Classics.