The famous philosopher known for advocating the separation of powers in government is Montesquieu. In his landmark work "The Spirit of the Laws," published in 1748, he argued that political power should be divided among separate branches of government—executive, legislative, and judicial. This separation was essential to prevent any one branch from gaining too much power, thereby protecting individual liberties and ensuring a system of checks and balances. Montesquieu’s ideas greatly influenced the framers of the U.S. Constitution, contributing to the framework of modern democratic governance and the protection of civil rights.