3rd Century B.C. Genius
Archimedes lived from 287 to 212 B.C., a generation after Euclid. During his 75 years, Archimedes did a lot: the laws of buoyancy, invention of really big numbers (to show that the number of grains of sand in the universe is finite), the science of hydrostatics, and invention of the screw. In fact, Archimedes' screw is still used as a primitive manual pump in many Third-World countries. And he was the first one to give an accurate approximation of pi.
Archimedes is also known for his ingenious methods used in the defense of Syracuse against the Roman invaders. He was in this sense an early precursor of Leonardo da Vinci. He is apparently the first to apply mathematics to physics, inventing the hybrid "mathematical physics" well in advance of the "modern" Galileo.