Jack L. Tilley is an American businessman and retired United States Army soldier. He served for almost 37 years in the United States Army, culminating in his appointment in 2000 as the 12th Sergeant Major of the Army, a post he held until his retirement on January 15, 2004. He was the last Vietnam War veteran to serve in that position.

The sergeant major of the Army (SMA) is a unique non-commissioned rank and position of office in the United States Army. The holder of this rank and position is the most senior enlisted soldier in the Army, unless an enlisted soldier is serving as the senior enlisted advisor to the chairman. The SMA is appointed to serve as a spokesman to address the issues of enlisted soldiers to all officers, from warrant officers and lieutenants to the Army's highest positions. As such, they are the senior enlisted advisor to the chief of staff of the Army. The exact duties vary depending on the chief of staff, though much of the SMA's time is spent traveling throughout the Army, observing training and talking with soldiers and their families.