Stanisław Ulam

Stanisław Marcin Ulam (April 13, 1909 – May 13, 1984) was a Polish mathematician who took part in the Manhattan Project and proposed the design used for most thermonuclear weapons. 
He also proposed using nuclear explosions to propel rockets, and he developed several mathematical tools in number theory, set theory, ergodic theory and algebraic topology. Above all, he is known by being a coauthor (with Nicholas Metropolis) of the Monte Carlo algorithm.
Ulam was of Jewish descent.