The bastard who keeps everything running and in line with their own special brand of thinking that may seem nonsensical to all those who don't know how the majestic Corporal's mind works as they keep things running smoothly and keeps the other NCO's in check.
A Noncommissioned Officer (NCO) in various armed forces, of a rank immediately below sergeant, or, in Canada, a master corporal. Also the rank above a Private.
Lawrence: Hey I just got promoted from a Private!
Jason: Oh! Now you're a Corporal!
GO ARMY.