Geoffrey Hinton - Was one of the first researchers who demonstrated the use of generalised back propagation algorithm for training multi-layer neural nets.
Archimedes (212 BC) - Used a lot of advanced methods (something like infinitesimal calculus) which he used to derive the formulas for computing the volume of cones and other solids of revolution, he also used similar methods to investigate the properties of conics.
Eratosthenes (194 BC) - Known for the Sieve of Eratosthenes, which is a method of finding prime numbers.
Euclid (300 BC) - Mathematical treatment of “preferred outcomes” or utility was first finalised by him, gave the basis for modern proof-based mathematics.