Wikipedia
General of the Armies
The General of the Armies of the United States, or more commonly referred to as General of the Armies (abbreviated as GAS), is the highest possible military rank in the United States Armed Forces. The rank is informally equated to that of a six star general and is the highest possible operational rank of the United States Army.
The rank has only been held twice in history - once by an active duty officer ( John J. Pershing) with a further posthumous promotion to George Washington in 1976. The rank of General of the Armies is senior to General of the Army, General of the Air Force and Fleet Admiral.