Who is Sergeant "Horrible" Hanley from Private Peaceful and what is their importance?

Sergeant "Horrible" Hanley is Charlie and Thomas trainer in boot camp. He drives them day in and day out, never letting up. Right from the start, Charlie refuses to play along with Hanley's mean jokes. Everyone else is afraid of him, and calls him Horrible Hanley. Hanley punishes Charlie by lashing him to the gun wheel all day while the others train. From then on, he seems to have it in for Charlie and Thomas.