Short answers, pulled from the story.
Aristotle wrote a book called Politics that described how states cycle through different forms of government. He proposed mixing monarchy, aristocracy and democracy to create stability instead of allowing pure forms to descend into anarchy or tyranny.
Polybius identified three distinct powers within Rome's structure where monarchical consuls held executive authority, aristocratic Senate families deliberated, and democratic assemblies functioned through elections. Each institution checked and balanced the others to guarantee long-term stability and prosperity.
The constitution of Britain during the Victorian Era combined these elements following events like the Civil War known as the Puritan Revolution and the Glorious Revolution which took place in 1688. This system had roots in seventeenth-century England's political upheavals including the exclusion crisis between 1679 and 1681.
James Madison called himself the father of the American constitution in Federalist Paper No. 40 and stated that the Constitutional Convention of 1787 created a mixed constitution. He referred to Polybius in Federalist Paper No. 63 when discussing Roman influences on this arrangement.
One school of scholarship holds that the Senate represents aristocracy since senators were elected starting in 1912. The House of Representatives embodies direct democratic election while the President represents rule by one through the executive branch.