Socrates 469 BC–399 BC Philosopher Socrates wasCondemned to Death by Hemlock

The most interesting and influential thinker in the fifth century was Socrates, whose dedication to careful reasoning transformed the entire enterprise. Since he sought genuine knowledge rather than mere victory over an opponent, Socrates employed the same logical tricks developed by the Sophists to a new purpose, the pursuit of truth. Thus, his willingness to call everything into question and his determination to accept nothing less than an adequate account of the nature of things make him the first clear exponent of critical philosophy.
Although he was well known during his own time for his conversational skills and public teaching, Socrates wrote nothing, so we are dependent upon his students (especially Xenophon and Plato) for any detailed knowledge of his methods and results. The trouble is that Plato was himself a philosopher who often injected his own theories into the dialogues he presented to the world as discussions between Socrates and other famous figures of the day. Nevertheless, it is usually assumed that at least the early dialogues of Plato provide a (fairly) accurate representation of Socrates himself.

http://www.historyforkids.org/learn/greeks/philosophy/socrates.htm
http://wsu.edu/~dee/GREECE/SOCRATES.HTM