Who is Sergeant R--- from Wind, Sand and Stars and what is their importance?

The most remarkable man Antoine has the chance to observe in his soldiering in the Spanish civil war is Sergeant R—-. He prepares willingly to lead his men into battle with near certitude that he will be killed in the effort. Antoine inquires after his entering the army, and the sergeant describes his life as an accountant and the compelling obligation he felt for the cause for which so many of his friends were uniting. Antoine wonders what would inspire in a man such a willingness to die and discovers in the sergeant that it is love for his country and his fellow soldiers that awakens the warrior within him.