Pythagoras, an introduction

And the end of all our exploring will be to arrive where we started,
And know the place for the first time.
     --T.S. Eliot, Ash Wednesday

Pythagoras: 570-c. 495 BC. Buddha is his contemporary.

These three men wrote about Pythagoras:
Porphyry (233-305 C.E.), a student of Plotinus
Iamblichus (250-325 C.E.): On the Pythagorean Life
Diogenes Laertius
Some of Plato's dialogues directly reflect Pythagorean thought. Aristotle wrote specifically about it.