The rank of brigadier general has existed in the United States armed forces since the American Revolutionary War. A brigadier general was, at first, strictly an infantry officer who commanded a brigade; however, over the course of the 19th and 20th centuries, the responsibilities of the rank expanded significantly.
During the period from March 16, 1802 to January 11, 1812, the rank of major general was abolished and brigadier general became the highest rank in the U.S. Army. Foreseeing the need for an expanded general staff in case of war, which seemed imminent, Congress restored the rank of Major General in January 1812.
The insignia for a brigadier general is one silver star worn on the shoulder or collar, and has not changed since the creation of the rank two centuries ago. Since the Mexican-American War, however, the lower rank of colonel has been the normal rank appointed to command a brigade that is organic to a division (e.g., the 1st Brigade of the 94th Infantry Division, vice the 187th Infantry Brigade).
Today, an Army “BG” typically serves as Deputy Commander to the Commanding General of a division or division-sized units and assists in overseeing the planning and coordination of a mission. In an infantry brigade not organic to a division, a brigadier general serves as the unit’s commander, while a colonel serves as deputy commander.
Additionally, one-star officers of all services may serve as high-level staff officers in large military organizations.