Final answer:
The three key Federalists were Alexander Hamilton, John Jay, and James Madison, who co-authored The Federalist Papers.
Step-by-step explanation:
The three key Federalists were Alexander Hamilton, John Jay, and James Madison. They co-authored a series of essays known as The Federalist Papers, which were published to persuade the public to support the new Constitution. These essays explained the importance of a strong central government and the checks and balances system to prevent tyranny.