Final answer:
The Joint Chiefs of Staff includes the Chief of Staff of the Army, Chief of Naval Operations, Chief of Staff of the Air Force, and the Commandant of the Marine Corps, who are principal military advisors to the President and other key officials.
Step-by-step explanation:
The Joint Chiefs of Staff (JCS) consist of the senior military officers from various branches of the United States Armed Forces. This group includes the Chief of Staff of the Army, Chief of Naval Operations, Chief of Staff of the Air Force, and the Commandant of the Marine Corps. Each of these individuals serves as a principal military advisor to the President, the Secretary of Defense, and the National Security Council.