Von Neumann: The Interaction of Mathematics and Computing by Stanislaw M. Ulam (1976)
Stanislaw M. Ulam, the Polish-American mathematician, who is probably most famous for discovering a means of making thermonuclear weapons, was also the close personal friend of John Von Neumann, considered the mathematical founder of digital computation, having built the first flexible, programmable digital computer. Ulam was a close collaborator with his friend on the mathematical basis of this work.
Perhaps the greatest contribution to science made by Ulam was his development of the Monte Carlo Method, an important calculational tool in understanding neutron diffusion in materials, that later has found applications in many areas, from evolutional biology, to drug development in applications involving protein folding, finance, and many other fields.
Less well known is the role Ulam played in the development of the hydrodynamic calculations for the implosion plutonium device tested at Trinity and dropped on Nagasaki, work that was supported by Von Neumann's initial work to understand the dimensionless Reynolds number in fluids where the boundary between laminar flow and turbulent flows. As described in the video lecture below, these speculations led to the thinking that resulted in the digital computer.
Ulam came to the United States in 1935 at the invitation of Von Neumann to work at the Institute of Advanced Study at Princeton.
Von Neumann died in 1957 and is buried in Princeton. On his deathbed Von Neumann, from a family of non-practicing Jews, converted to Catholicism to satisfy Pascal's Wager.
Below is an interesting video of an informal talk Ulam gave at Los Alamos about his friend, and the mathematical origins of the digital computer. Ulam had originally intended his autobiography, Adventures of a Mathematician to be a biography of Von Neumann. A film version of this work has been produced and is worth watching, I think.
In 1976, in a lecture series on computation and Von Neumann at Los Alamos, Ulam, who had returned to pure mathematics after his weapons work, gave the informal talk in the video below.