Final answer:
Command Sergeant Major William Joe Gainey was the 1st Senior Enlisted Advisor to the Chairman Joint Chiefs of Staff (SEAC), serving from 2005 to 2008.
Step-by-step explanation:
The 1st Senior Enlisted Advisor to the Chairman Joint Chiefs of Staff (SEAC) was Command Sergeant Major William Joe Gainey. He served as the SEAC from October 1, 2005, until April 25, 2008.
This position was established to advise the Chairman on all matters concerning joint and combined total force integration, utilization, health of the force, and enlisted professional development.
Gainey was the first enlisted service member to serve as a senior advisor to the Chairman, making his role particularly significant in the representation of the enlisted perspective at the highest levels of command.