Which person was a military officer during the civil war and later in 1876 command U.S troops in the battle of Little Bighorn?

The military officer you are referring to is George Armstrong Custer. He served as a Union cavalry officer during the Civil War and gained fame for his aggressive tactics. In 1876, he commanded U.S. troops in the Battle of Little Bighorn, where he and his forces were defeated by Native American tribes led by leaders such as Sitting Bull and Crazy Horse. This battle became one of the most famous events in American history.