Who came up with the separation of powers idea?

The idea of the separation of powers is most commonly attributed to the French philosopher Montesquieu, who articulated it in his 1748 work "The Spirit of the Laws." He argued that political authority should be divided among different branches of government—typically the legislative, executive, and judicial—to prevent any one branch from becoming too powerful. This concept significantly influenced the framers of the U.S. Constitution and many other democratic systems worldwide.