Alexandre Lyapunov was a prominent Russian mathematician and physicist, born on June 6, 1857, in Yaroslavl, Russia. He is best known for his contributions to the fields of stability theory and dynamical systems. His work laid the foundation for what is now known as Lyapunov stability, which helps determine the stability of equilibrium points in differential equations. Lyapunov's most significant achievement is the development of the Lyapunov function, a mathematical tool used to analyze the stability of systems. He published several influential papers and books, including "The General Problem of Stability of Motion," which remains a key reference in control theory and applied mathematics. He passed away on November 3, 1918.