Himmelstoss turns vicious
Himmelstoss is a puzzle. At the beginning of the Second Company's basic training, he appears to be an okay drill sergeant, teaching the young men the basics of soldiering. He remembers this is the same bunch of high school kids who teased him in the town square but they didn't hurt him except to embarrass or annoy him. In the beginning, it seems like Himmelstoss doesn't hold a grudge, but in fact he does. Apparently, Himmelstoss's resentment re-appears and boils up, making him vicious and start to abuse the young recruits far, far more than they did to him.
That's the mystery. The recruits did nothing to stir up Himmelstoss's resentment. It happened all on his own. Himmelstoss eventually goes too far with another company and is sent to the front as a corporal. At first afraid as a new soldier, he gains his wits and actually earns a commendation. At the movie's end we learn from Paul, writing a letter to Albert, that Himmelstoss was killed in action.
Lastly, Himmelstoss may have had a small man's complex. Strange, that for a German, he should be so short, probably 5'4" or 5'5", standing next to Paul Baumer (Richard Thomas) who is 5'8-1/2" tall.