Jakob Bernoulli
One of the Bernoulli family, and best known for his work Ars Conjectandi (1713) on probability ("Jacques" is the same as Jakob). In this posthumous work, he developed the theory of combinations, and proved the first (weak) law of large numbers. However, his theorem covered only the case in which we estimate an integral ratio (a rational number) of an event. His name is commemorated by such terms as "Bernoulli trials", which signifies a series of experiment (such as coin-tossing) with two discrete outcomes, "success" and "failure". The probability distribution for such cases are called "binomial distribution".
See a Biography in MacTutor History of Math.