The traditional dates of Plato's lifespan are 428 BCE to 348 BCE. He was born in Athens to an aristocratic and well-to-do family. While Plato was still young, his father died and his mother re-married Pyrilampes, a friend of Pericles, the great Athenian statesman. It is likely that Plato fought in the Athenian army against Sparta; he was eighteen in 409, when the Pelopennesian War was still waging.
From early age, Plato was familiar with political life because of his mother's connections and his social class. It was probably expected, in fact, that Plato would enter politics as an intelligent young man of the ruling class. However, a pair of events turned Plato away from politics entirely. The first was the assumption of power by the Four Hundred and the Thirty, groups of powerful, wealthy citizens who seized control at the end of the Pelopennesian War and turned Athens into an oligarchy. Plato's feelings about the political takeover may have been mixed, as he was related to Charmides, one of the Thirty, but he certainly did not approve of such a government (which was tyrannical and unstable), even at a young age. But whatever relief he might have felt about the restoration of the Democracy disappeared when it executed his mentor, Socrates. There was no place for Plato in practical politics. The caution that Plato avows for anything but his Just government, and of democracy in particular, can perhaps be explained by these biographical details.
There is no question that Socrates was an enormously important intellectual influence on Plato's work. The essential difference between Plato and Socrates is in scope--Socrates arguments were limited to a discussion of ethics--whereas Plato's work includes epistemology, metaphysics, political science, and ethics. Plato's work, therefore, can be divided into three segments: early, middle, and late. In the early dialogues, also called the Socratic dialogues, Socrates and his elenchus still play a defining role in the philosophical discourse.