Nathan Brittles, as the movie opens, is a 62-year old Captain in the United States Army, serving in the Cavalry branch (normally referred to simply as the U.S. Cavalry). He was born in 1814 in what was then the Indiana Territory (he mentions growing up on the banks of the Wabash River). He left his home in his late teens to join the Cavalry and eventually attained officer rank, probably while serving as an NCO in combat. He served in various Indian Conflicts, as well as both the Mexican War and in the Eastern Theater during the Civil War (he mentions Bull Run and Gettysburg). He had probably attained the rank of Colonel during the Civil War and commanded his own volunteer regiment, but reverted to lower rank when returning to the regular Army. He has obviously commanded the same Troop at the same post for many years (his family that had died nine years earlier were buried there). He faced mandatory retirement due to age, but was granted a reprieve at the very end of the movie by President Grant, who promoted him to Lieutenant Colonel and reassigned him to Washington as Chief of Scouts.