Blaise Pascal and Pierre de Fermat are considered the fathers of modern probability theory. The earliest known work on probability theory was done by Girolamo Cardano, an Italian mathematician and physicist born in 1501. However, his manual on probability and gambling, "Liber de Ludo Aleae," was not published until 1663.
Blaise Pascal and Pierre de Fermat began discussing probability via correspondence in 1654. Although Cardano's work pre-dated theirs, Pascal and de Fermat's laid the foundation of modern probability theory through their solution to the "problem of points." They devised a consistent solution for the division of stakes for a game of chance that is interrupted before its agreed upon conclusion. This provided insights into probability that are still influential today.