One of the best know people of mathematics and geometry. He is known mostly for the Pythagorean Theorem for right triangles.
Although we do not know the exact dates he lived (570 BC to 490 BC), he was influential in the philosophical thinking of the Athenian Greeks and Western civilization. https://en.wikipedia.org/wiki/Pythagoras
Much more can be said by going to https://en.wikipedia.org/wiki/Pythagoras or https://plato.stanford.edu/entries/pythagoras