What's known is that "War Eagle" is to Auburn what "Roll Tide" is to Alabama -- a greeting Auburn athletes and students use to identify and connect with one another. But no one seems to know where it came from.
One popular theory is that a soldier from Alabama was the sole Confederate survivor of a particularly bloody Civil War battle. Somewhere in that battle, he came across a wounded eagle whom he nursed back to health. Returning to Auburn, where the soldier went to school, as a faculty member, he brought the eagle on campus with him. The eagle was then said to have circled overhead, exciting fans, at Auburn's first game of the 1892 season.
Like Georgia, who uses actual bulldogs as its mascot, Auburn has had seven numbered War Eagles over the years. The latest was officially named War Eagle.