Most people have heard of the Greek philosophers Socrates, Plato and Aristotle. Both Plato and Aristotle had a major influence on the Christian Church whether via Neo-Platonism (Plotinus) or Christian scholasticism (Thomas Aquinas) in the Middle Ages. Jewish scholasticism was likewise kindled by Aristotle (Moses Maimonides) whose philosophical interests, like those of Aquinas, were built on the efforts of Avicenna and Averroes to translate the writings of Aristotle into Arabic where, courtesy of the efforts of Al-Kindi and Al-Farabi, they formed a major part of early Islamic philosophy.
Howerver 50-100 years before Socrates (Plato's famous mentor) held sway, Greece had seen the emergence of a mumber of philosophical schools which are generally regarded as the true forebears of Western philosophy. (To put this into context, this is roughly the same era as the post-exilic prophets in Israel.)
Apart from the mathematician Pythagoras, their names are largely unknown outside professional philosophical circles. This is an enormous pity as their ideas have as much relevance now as they did in their own time, indeed perhaps even more so in the era of black holes, quantum mechanics and artificial intelligence.
Although dismissed by Friedrich Nietzsche, the Pre-Socratics have influenced philosophers as ideologically opposed as Karl Marx and Karl Popper!
There are several excellent introductions to the Pre-Socratics including:
Jonathan Barnes, The Presocratic Philosophers G. S. Kirk, J. Raven & M Schofield The Presocratic Philosophers: A Critical History with a Selection of Texts Also Stanford University has an excellent online resource in its Encyclopedia of Philosophy, namely: