Montesquieu, full name Charles-Louis de Secondat, Baron de La Brède et de Montesquieu, was an influential French philosopher and political thinker of the Enlightenment era, born on January 18, 1689, and died on February 10, 1755. He is best known for his work "The Spirit of the Laws" (1748), which articulated the theory of separation of powers—a concept crucial to modern democratic governance. Montesquieu's ideas significantly impacted the formation of constitutions around the world, including the United States Constitution.