Senior Enlisted Advisor to the Chairman

The senior enlisted advisor to the chairman of the Joint Chiefs of Staff (SEAC ) is the most senior enlisted position in the United States Armed Forces and is a unique enlisted rank which only one individual may hold at any given time. The SEAC is appointed by the chairman of the Joint Chiefs of Staff to serve as a spokesperson to address the issues of enlisted personnel to the highest positions in the Department of Defense.

Source: Wikipedia — Senior Enlisted Advisor to the Chairman (CC BY-SA 4.0)