The narrator

The main character in the short story "Ambush" by Tim O'Brien is the unnamed narrator.

The narrator’s outer characterization is completely missing. We know that he served in the Vietnam War and has a nine-year-old daughter, so we can assume that he is middle-aged. His name is not mentioned. The lack of a physical description and name suggest that the narrator could be a symbolic representation of all the veterans who are still troubled by memories of wars. 

The narrator's inner characterization is the focus of the story, and it serves to draw attention to the traumas soldiers can experience during wars. The narrator is deeply troubled by memories of war, particularly of one event in which he killed a young man with a grenade.

When he sees the young man approach, the narrator’s mind goes blank, and he reacts automatically (ll. 35-38). He points out from the start that his action was not prompted by duty and that he threw the grenade out of panic, without actually realizing the true implication...