Plato (Greek: Πλάτων) was an ancient Greek philosopher of the Classical period, considered a foundational thinker in Western philosophy and an innovator of the written dialogue and dialectic forms. He influenced all the major areas of theoretical philosophy and practical philosophy, and was the founder of the Platonic Academy, a philosophical school in Athens where Plato taught the doctrines that would later become known as Platonism.

Plato's most famous contribution is the theory of forms (or ideas), which aims to solve what is now known as the problem of universals. He was influenced by the pre-Socratic thinkers Pythagoras, Heraclitus, and Parmenides, although much of what is known about them is derived from Plato himself.

Along with his teacher Socrates, and his student Aristotle, Plato is a central figure in the history of Western philosophy. His complete works are believed to have survived for over 2,400 years—unlike nearly all of his contemporaries. Although their popularity has fluctuated, they have consistently been read and studied through the ages. Through Neoplatonism, he also influenced both Christian and Islamic philosophy. In modern times, Alfred North Whitehead noted: "the safest general characterization of the European philosophical tradition is that it consists of a series of footnotes to Plato."