Pythagoras - He is credited with developing the Pythagorean Theorem, which states that in a right triangle, the square of the hypotenuse is equal to the sum of the squares of the other two sides. He is also credited with important contributions to geometry, including the concept of similarity and the five regular solids. He famously believed that all numbers were related to the divine, and his school of thought, Pythagoreanism, greatly influenced later mathematicians.