The 12th Man is a tradition at Texas A&M University that began in 1922 during a football game against Centre College, the nations top-ranked team at the time. During the game, the Aggies were plagued by injuries, and the coach called upon E. King Gill, a former football player who was in the stands, to suit up and stand ready to play if needed. Although Gill never entered the game, his willingness to serve his team has been passed down from generation to generation of Aggies for nearly one hundred years, and the entire student body at A&M is now considered the 12th Man.

The 12th Man is always in the stands waiting to be called upon if they are needed, and they stand during the entire game to show their support. This tradition took on a different look in the 1980s when Coach Jackie Sherrill started the 12th Man Kick-Off Team composed of regular students through open tryouts. Later, Head Coach R.C. Slocum changed the team to allow only one representative of the 12th Man on the kick-off team.

The 12th Man tradition also took musical form. The 12th Man sings a song after each game in which the Aggies are outscored. In October 1998, a new 12th Man tradition began called Maroon Out, where the student body created a sea of maroon spirit throughout the stands by wearing maroon t-shirts bearing the words Maroon Out.

The first known instance of Texas A&M referring to its fanbase as the "12th Man" is contained on page 17 of the November 25, 1921, edition of The Battalion, the Texas A&M campus newspaper). The 12th Man is a registered trademark of Texas A&M University, and the university has taken legal action against other organizations that have used the term without permission).