Why is Pythagoras called a philosopher?

Pythagoras was one of the most ancient philosophers of antiquity. He was engaged in the knowledge of the world. All his teachings can be divided into two parts: a religious and mystical way of life and a scientific approach to understanding the world. Also Pythagoras was the founder of the school of Pythagoreanism. The philosopher himself lived in the 6th century BC. His activities became the impetus for the development of the teachings of later philosophers, such as Socrates, Plato, Aristotle.