I would say an iconic performance in Full Metal Jacket. Seemed like a pretty great guy from interviews and such that I've seen.
Funny anecdote, after completing NCO school and returning to my unit for the rest of my service 10 years ago, and before new recruits stepped in, our unit commander said he does not want any of us NCOs playing Sgt Hartmans. Naming him specifically.
Of course, this was not in a war-going army but the day-care center that is the Finnish Defense Forces