Socrates' teachings challenged the established religion. He was accused on introducing new gods, refusing to recognize the established religion, and corrupting the youth. He was tried and found guilty. Sentenced to death Socrates drank a cup of poison hemlock in 399.
Socrates himself did not leave any written record, so for details of his life and philosophy we have to look at the writing of contemporaries. Here are the three main ancient Greek sources on Socrates:
PlatoPlato was a student of Socrates and the major ancient source used for details about Socrates' method because in the dialogues Plato wrote, Socrates led the discussions. When Socrates died, Plato wrote an apology explaining Socrates' position, and started the philosophical school known as the Academy.
Plato was born around May 21 in 428 or 427 B.C. He was related to Solon and could trace his ancestry to the last legendary king of Athens, Codrus.
XenophonXenophon was born in Athens during the early years of the Peloponnesian War. He may have been one of Socrates' students, but he was involved in the war in the Persian Empire he wrote about in the Anabasis when Socrates was executed. Some years later, Xenophon wrote a defense of Socrates against the charges that led to his execution. Like Plato, Xenophon wrote a Symposium featuring Socrates at the Greek dinner party. Socrates is alse featured in Xenophon's Economics.
AristophanesUnfortunately, we know very little about Aristophanes (c. 448-385 B.C.), although he lived in Athens during periods of turmoil, beginning his writing career after the death of Pericles. He portrayed Socrates as a sophist in his comedy, The Clouds. This negative portrayal of Socrates contrasts with the positive ones of Socrates' two students.
"Of the two alternate portraits of Socrates, that of Aristophanes seems the more difficult to resuscitate for several reasons. First, Aristophanes' The Clouds is a comedy, and comedies are not the first place the serious scholar would turn to derive an accurate depiction of an historical figure. Second, the depiction of Socrates in this work seems so at odds with what we know of Socrates from other sources that we seem compelled to dismiss it as caricature. Finally, the Socrates of both Xenophon and Plato explicitly denies the type of activity that The Clouds demonstrates him as engaged in."
Bryn Mawr Classical Review 95.06.16 Paul A. Vander Waerdt (ed.), The Socratic Movement.