The life and teachings of Socrates (c. 469-399 B.C.) stand at the foundation of Western philosophy. He lived in Athens during a time of transition (Athens' defeat at the hands of Sparta in the Peloponnesian War (431-404 B.C.) ended the Golden Age of Athenian civilization) and had a tremendous influence on the Athenian youth of his day. Socrates himself never recorded his thoughts, so our only record of his life and thought come from his contemporaries. It seems he led a very simple life, renouncing wealth and holding himself aloof from political ambitions, preferring rather to mingle with the crowds in Athens' public places, engaging whomever he could in conversation. In 399, Socrates was brought before a jury of around 500 Athenians on charges of not recognizing the gods recognized by the state, of inventing new deities, and of corrupting the youth of Athens. The most likely reason for this trial would be Socrates' close association with a number of men--Alcibiades being one of them--who had fallen out of favor in Athens. Since an amnesty had been declared on political offenders, other charges had to be brought against him. Socrates was found guilty by a narrow margin and then sentenced to death.
Plato (c. 427-347 B.C.) was one of Socrates' greatest admirers, and our knowledge of Socrates stems mostly from Plato's dialogues. Plato was born into a prominent Athenian family, and would have been expected to pursue a career in politics. However, the short-lived Spartan-imposed oligarchy of the Thirty Tyrants (404-403) and the trial and execution of his mentor Socrates led Plato to become disgusted with the Athenian political life, and he devoted himself instead to teaching and philosophical inquiry. To that end, he founded the Academy around 385 B.C., an institution that numbered Aristotle among its students. The Academy lasted in some form until 527 A.D., and has served as the prototype for the Western university system.
Plato's thought is mostly recorded in the form of dialogues that feature Socrates as the protagonist. Though we can't be certain as to the specific dates of composition, Plato's dialogues can generally be classed into early, middle, and late periods. The early dialogues were written soon after Socrates' death, and in them we get the clearest picture of Socrates and Socratic philosophy. As Plato matured, however, he developed an increasingly distinct voice and philosophical outlook. In these middle and late dialogues, of which the Symposium is one, the figure of Socrates serves more as a mouthpiece for Plato's own views. For instance, there is brief mention in the Symposium of the Theory of Forms, which is entirely Plato's invention. The complex framing devices set up by Plato at the beginning of the dialogue are meant in part to suggest the fictionality of the account.