Staff sergeant

Staff sergeant is a rank of non-commissioned officer used in several countries. The origin of the name is that they were part of the staff of a British army regiment and paid at that level rather than as a member of a battalion or company.

U.S. Army
Staff sergeant (SSG) is E-6 rank in the U.S. Army, just above sergeant and below sergeant first class, and is a non-commissioned officer. Staff sergeants are generally placed in charge of squads, but can also act as platoon sergeants in the absence of a sergeant first class. In support units, staff sergeants ordinarily hold headquarters positions because of the number of slots available for them in these units. Staff sergeants are typically assigned as a squad leader or company operations non-commissioned officer in charge at the company level, but may also hold other positions depending on the type of unit. Staff sergeants are referred to as "Sergeant" except for in certain training environments and schools. The NATO code is OR-6.

History
The rank of staff sergeant in the U.S. Army (along with technical sergeant (renamed sergeant first class in 1948) and master sergeant) was created by Congress after the First World War.