Gérard Debreu was a French economist and mathematician, born on July 4, 1921, and passed away on December 31, 2014. He is best known for his work in the field of economic theory, particularly for his contributions to the concept of general equilibrium. Debreu's research helped to formalize how supply and demand interact in markets, earning him the Nobel Prize in Economic Sciences in 1983. Debreu's influential book, "Theory of Value," published in 1959, laid the groundwork for modern economic analysis. His work has had a lasting impact on both economics and mathematics, bridging the gap between these two disciplines. Through his rigorous approach, Debreu advanced the understanding of how economies function and the role of mathematical models in economic theory.