William Feller was a prominent Croatian-American mathematician known for his significant contributions to probability theory. Born on July 7, 1906, in Zagreb, he later moved to the United States, where he became a professor at Princeton University. Feller's work laid the foundation for many modern concepts in probability and stochastic processes. Feller is best known for his influential books, including "An Introduction to Probability Theory and Its Applications." His research addressed various topics, such as Markov processes and random walks, and he played a crucial role in developing the mathematical framework for these areas. He passed away on January 14, 1970.