Siméon Denis Poisson was a French mathematician and physicist born on June 21, 1781. He is best known for his contributions to probability theory and mathematical physics. His work laid the foundation for many concepts in statistics and is widely used in various fields, including engineering and economics. One of Poisson's most significant achievements is the Poisson distribution, a probability distribution that expresses the probability of a given number of events occurring in a fixed interval of time or space. He also made important contributions to mechanics and electromagnetism, influencing future generations of scientists and mathematicians. Poisson passed away on April 25, 1840.