Final answer:
The Federal Reserve serves as the central bank for the United States, acting as an agent of the US Treasury and conducting monetary policy.
Step-by-step explanation:
The entity that acts as the agent of the US Treasury as the nation's central bank is the Federal Reserve, often abbreviated as "the Fed."
The Federal Reserve is responsible for conducting monetary policy, ensuring financial system stability, providing banking services to commercial banks and depository institutions, and serving the federal government.
Unlike most central banks, the Federal Reserve has a unique structure that is semi-decentralized, with a mix of government appointees and private-sector bank representation, emphasizing independence from political pressure to focus solely on economic merits.