Pythagoras of Samos is one of the most amazing figures in the history of ideas. His picture of a harmonious and number-driven world—a fusion of scientific and mystical worldviews—has had a profound influence on all of Western culture. Pythagoras was the leader of a political and religious sect (the first group of its kind that we know of) that had enormous influence in various regions of Greece. He is credited with one of the most important discoveries of antiquity: the equality of the sum of the squares of the legs and the square of the hypotenuse in a right triangle. This true geometric treasure not only has many practical consequences, but also marks, among other things, the birth of mathematics as an independent rigorous discipline.