Recognition is due the following people, from whom great philosophical thoughts emerged:
Thales: Traditionally considered the first ever western philosopher. None of his writings survive.
SOCRATES: Ancient Greek, changed philosophy from a study of natural science to ethics and politics. Wrote nothing.
PLATO: Ancient Greek, student of Socrates, most influential philosopher of all time. Works: The Republic.
ARISTOTLE: Ancient Greek, student of Plato, second most influential philosopher of all time. Works: The Nichomachean Ethics, The Metaphysics, The Politics.
http://www.elliotcross.com/great.html