Pierre-Simon Laplace's contributions to mathematics and physics are so vast that he was called the 'French Newton.' His Théorie analytique des probabilités put probability theory on a rigorous mathematical foundation, introducing many of the formulas still used today. He proposed that if you knew the position and velocity of every particle in the universe, you could mathematically predict the entire future -- a thought experiment now called Laplace's demon. His celestial mechanics proved the long-term stability of the solar system, and his Bayesian approach to probability underpins modern machine learning, spam filters, and medical diagnosis.