What sort of man was the sniper at the start of the story?

At the start of the story, the sniper is described as a seasoned soldier. Although he is young ("face of a student"), his demeanor makes him look like an older solider, one who has become "used to looking at death." He has the "cold gleam of the fanatic." His stare indicates that he is no longer the naive student his youth might indicate. At this point, he is a focused, intense soldier/machine. 

Even though he is this seasoned soldier, he does make mistakes. When he lights the cigarette, he gives away his position. However, he recovers from this mistake and manages to take out an informer (old woman), the soldier in the turret, and his enemy sniper on the other rooftop. Even when he gets hit (by the enemy sniper), he manages to dress the wound himself, despite the immense pain: 

Then taking out his field dressing, he ripped open the packet with his knife. He broke the neck of the iodine bottle and let the bitter fluid drip into the wound. A paroxysm of pain swept through him. He placed the cotton wadding over the wound and wrapped the dressing over it. He tied the ends with his teeth. Then he lay still against the parapet, and, closing his eyes, he made an effort of will to overcome the pain. 

Toward the end of the story, the sniper does have moments of sensitivity, remorse, and humanism. But in the beginning, and for most of the story, he is a disciplined machine of a soldier.