Plato (427—347 B.C.E.) was an ancient Greek philosopher who lived in the wealthy and powerful city state of Athens. He himself came from a wealthy and well-connected family. Plato was introduced to philosophy by Socrates, an influential thinker who left behind no written works. Plato founded the Academy, a philosophical school that can be considered the first university.
Most of Plato's works are written in the form of dialogues, in which small groups of characters (mainly based on real people, especially on Socrates and his circle) discuss big philosophical ideas such as the nature of the world, the soul, language, ethics, and knowledge. Because all of Plato's works are written as dialogues, it is not always obvious what position Plato himself supports. Instead, the purpose of each dialogue seems to be to explore all aspects of a small group of related questions to stimulate the reader to think about the subject for herself.
Perhaps the central question in Platonic philosophy is how we can have certain knowledge, given that we live in a world that is constantly changing.