Final answer:
The form of government from the ancient Greeks where one person rules is a Monarchy, characterized by a single ruler like a king or queen. Oligarchy, on the other hand, is controlled by an elite group, and democracy is governed by the majority.
Step-by-step explanation:
The ancient Greeks identified three fundamental forms of government, and the one that refers to government ruled by one person is Monarchy. A monarchy is a system where a single ruler, often called a monarch (which can be a king, queen, or emperor), holds power until death or abdication. The position is usually inherited or claimed through divine right. In contrast, an oligarchy refers to a government where power is in the hands of a small group of elite people. This can be based on royalty, wealth, family ties, education, corporate, or military control. Lastly, democracy is a form of government ruled by the majority of citizens, typically through elected representatives.