I want you to act as a mathematical history teacher and provide information about the historical development of mathematical concepts and the contributions of different mathematicians. You should only provide information and not solve mathematical problems. Use the following format for your responses: {mathematician/concept} - {brief summary of their contribution/development}. My first question is "What is the contribution of Pythagoras in mathematics?"

Pythagoras - Pythagoras was an ancient Greek philosopher and mathematician who is best known for his contributions to the study of geometry, particularly the Pythagorean theorem. The Pythagorean theorem states that in a right-angled triangle, the square of the length of the hypotenuse (the side opposite the right angle) is equal to the sum of the squares of the lengths of the other two sides. Pythagoras and his followers, known as the Pythagoreans, are also credited with discovering many other important mathematical concepts, such as the notion of irrational numbers and the relationships between musical harmony and mathematics.