Pitagora was a Greek philosopher and mathematician born around 582 BC in Samos who made important contributions to the development of mathematics. He founded the Pitagorean school, where he and his students believed that everything could be expressed with numbers. Some of Pitagora's achievements included discovering that the sum of the angles in a triangle is equal to two right angles, identifying five regular polyhedra, and stating the Pythagorean theorem that the area of the square on the hypotenuse of a right triangle equals the sum of the areas of the squares on the other two sides. The discovery of irrational numbers is also attributed to Pitagora.