Charles-Louis de Secondat, Baron de La Brède et de Montesquieu (18 January 1689 – 10 February 1755), was commonly known as Montesquieu. He was a French political thinker who lived during the Age Of Enlightenment. He is famous for his theory of the separation of powers in government. Many constitutions all over the world use it. He helped make the terms "feudalism" and "Byzantine Empire" popular.