Sergeant

In most non-naval military organizations, a sergeant is a non-commissioned officer (NCO) ranking above privates and corporals, and below warrant officers and commissioned officers.

There are usually several ranks of sergeant, each corresponding to greater experience and responsibility for the daily lives of the soldiers of larger units. Although even the highest sergeant is officially lower in rank than the lowest lieutenant, an experienced sergeant will have considerable personal power and know how to exercise it; a wise junior officer will heed the advice of the senior sergeant.

For instance, the US army has eight ranks of sergeant:

Sergeant Major of the Army
Command Sergeant Major (brigade and up)
Sergeant Major (battalion)
First Sergeant (company)
Master Sergeant
Sergeant First Class (platoon)
Staff Sergeant
Sergeant ("buck sergeant")

Many other militaries have ranks with similar names and duties, although the details are usually unique to each.