The influential figure behind the doctrine of "separation of powers" in government is Montesquieu. In his 1748 work "The Spirit of the Laws," Montesquieu argued for dividing government into three branches: executive, legislative, and judicial. This framework was designed to prevent any single branch from acquiring too much power, thereby ensuring checks and balances that promote democracy. His ideas significantly influenced the development of modern democratic governments, particularly the Constitution of the United States.