John von Neumann (1903–1957)
A probable genetic freak, due to a too-fast mind for math. Helped in the childhood of computer science, came up with pseudorandom number generators – a way to get a deterministically operated electric system (such as a computer) to output a random number, which is not as easy as it sounds.
Many things are named after von Neumann. For example, the idea of self-replicating machines that explore space, "Von Neumann probes". If alien civilizations exist, they may have launched one or more waves of such machines each, and what happens when they meet? Natural selection implies that the most ruthless machines would survive, which then implies (assuming there are many civilizations in the universe) that there's a sphere of von Neumann probes somewhere out there, expanding in all directions, eating all the planets and stars in their wake (to build more of themselves), potentially travelling near the speed of light so that we won't see them until they're already here.
After Stanislaw Ulam invented the modern version of Markov chain Monte Carlo, von Neumann immediately understood its importance and programmed the ENIAC to carry out Monte Carlo calculations (not MCMC?).
