Plato (428 - 347) 

Aristotle tells us that sometime during Plato's youth the philosopher-to-be became acquainted with the doctrines of Cratylus, a student of Heraclitus, who, along with other Presocratic thinkers such as Pythagoras and Parmenides, provided Plato with the foundations of his metaphysics and epistemology. Upon meeting Socrates, however, Plato directed his inquiries toward the question of virtue. It is difficult to determine the precise chain of events that led Plato to the intricate web of beliefs that unify metaphysics, epistemology, ethics and politics into a single inquiry. We can be certain, however, that the establishment of a government by Sparta (after the chaos of Athens' final defeat in 404), and the events that followed, dramatically affected the direction of his thinking.
The oligarchy made a practice of confiscating the estates of wealthy Athenians and resident aliens and of putting many individuals to death. In an effort to implicate Socrates in their actions, the Thirty ordered him to arrest Leon of Salamis. Socrates, however, resisted and was spared punishment only because a civil war eventually replaced the Thirty with a new and most radical democracy. Later, he was damned to die by the restored democracy.
At this point Plato left Attica with other friends of Socrates and spent the next twelve years in travel and study. Ater 399 Plato began to write extensively. Plato was forty the first time he visited Italy. Shortly thereafter, he returned to Athens and founded the Academy, located nearly a mile outside the city walls and named after the Attic hero Academus.
In 367 Dionysus of Syracuse died, leaving his son as the supreme ruler of a growing empire. Dion, his uncle and guardian, persuaded young Dionysus II to send for Plato, who was to serve as his personal tutor. Upon arriving, Plato found the situation unfavorable for philosophy, though he attempted to teach the young ruler anyway. In 365, Syracuse entered into war, and Plato returned to Athens. (Around the same time, Plato's most famous pupil, Aristotle, entered the Academy.)
In 361, Dion wrote Plato begging him to return. Reluctantly, Plato did so, setting out on his third and final voyage to Italy. But the situation had deteriorated beyond hope. Plato was soon spirited out of Syracuse from where he went back to Athens.
We know little of the remaining thirteen years in Plato's life. Probably sick of his wanderings and misfortunes in Sicily, Plato returned to the philosophical life of the Academy and, most likely, lived out his days conversing and writing. Pato died in 347, leaving the Academy to Speusippus, his sister's son. The Academy served as the model for institutions of higher learning until it was closed by the Emperor Justinian in 529 CE, almost one thousand years later.

links:  - selected links on Plato  - The Last Days of Socrates (bilingual: english and spanish)