What was Hamilton Madison and jay pen name?

Publius, short for Publius Valerius Publicola (Latin: Friend of the People), a Roman consul who helped overthrow the monarchy and establish the Roman Republic c. 500 BCE.

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The Federalist Papers were signed as "PUBLIUS", translated from Latin as "public". The intent in the signature is clear - the authors wanted to imply public interest in the debate; further, that the ideals in their works were not owned by an individual but by the public generally.