Plato (c. 428 - 348 B.C.) was a hugely important Greek philosopher and mathematician from the Socratic (or Classical) period. He is perhaps the best known, most widely studied and most influential philosopher of all time.
Together with his mentor, Socrates, and his student, Aristotle, he provided the main opposition to the Materialist view of the world represented by Democritus and Epicurus, and he helped to lay the foundations of the whole of Western Philosophy. In his works, especially his many dialogues, he blended Ethics, Political Philosophy, Epistemology, Metaphysics and moral psychology into an interconnected and systematic philosophy.
In addition to the ideas they contained (such as his doctrine of Platonic Realism, Essentialism, Idealism, his famous theory of Forms and the ideal of "Platonic love"), many of his writings are also considered superb pieces of literature.
Plato was the founder of the famous Academy in Athens, the first institution of higher learning in the western world. The philosophical school which he developed at the Academy was known as Platonism (and its later off-shoot, Neo-Platonism).