Short answers, pulled from the story.
Polybius wrote in his Histories, Book 6, that the Roman Republic was ruled by three distinct groups: the Roman Senate, the Consuls, and the Assemblies. This system prevented any single entity from holding unlimited power over the state.
John Locke published Two Treatises of Government in 1690 to outline his vision for political organization. He distinguished between legislative power, executive power, and federative power in Section 143 through Section 145 of the Second Treatise.
Montesquieu wrote The Spirit of Law in 1748 to describe the distribution of political power based on the Constitution of the Roman Republic and the British constitutional system. He argued each power should only exercise its own functions to prevent excessive centralization in a single monarch.
The Constitution of the United States implemented separation of powers in 1787 following years of debate. Alexander Hamilton wrote Federalist No. 78 to redefine the judiciary as a separately distinct branch before this implementation.
Bolivia, Costa Rica, Panama, Nicaragua, and Venezuela form their own distinct electoral branches. Taiwan uses a five-branch system introduced by Dr. Sun Yat-sen consisting of Executive Yuan, Legislative Yuan, Judicial Yuan, Control Yuan, and Examination Yuan.