Why is Plato (greek philosopher) famous?

Plato was a 4th-century BC Greek philosopher who gained perpetual notoriety for his contributions to the study of ethics and metaphysics. Plato was a student of Socrates--the Father of Western Philosophy--and his Dialogues are the primary resources for the study of Socrates' life and beliefs (Socrates did not write anything himself). 

Plato devoted his work to the study of the "forms," which were transcendent ideals such as Justice, Beauty, Truth, and Goodness. He placed an emphasis on the pursuit of virtue, which believed was the true path to happiness.

Plato founded his famed Academy in Athens circa 380; this center of learning became the model for the medieval and modern university system. Of Plato's many students, Aristotle is by far the most famous and influential. In addition to his own contributions to philosophy, Aristotle tutored Alexander the Great.