The famous philosopher who promoted ideas about separation of powers in government is Montesquieu. In his influential work, "The Spirit of the Laws", published in 1748, Montesquieu argued that government functions best when divided into three branches: the executive, legislative, and judicial. This division helps prevent the concentration of power and provides a system of checks and balances. His ideas significantly influenced the framers of the United States Constitution and modern democratic governance by emphasizing the importance of a structure that limits government authority and protects individual liberties.