Pythagoras (around 580-500 BC), Ancient Greek mathematician and philosopher. He was born in Samos, Greece, but left for Croton in Italy in around 520 BC. Here he founded his academy, which was largely dedicated to the study of the properties of numbers. As well as his famous theorem on right-angled triangles, his group discovered irrational numbers. These are numbers that cannot be represented as the ratio of two whole numbers. He discovered them after realising that the square root of two could not be represented in this way.