Who is Monsieur Stanislas Kapp from The American and what is their importance?

Monsieur Stanislas Kapp is the man Valentin duels. He is described as the bad natured son of a brewer. Rather than shoot Valentin in an area of his body that would not have proved fatal, Kapp shoots him in the chest. Kapp, on the other hand, only suffers a flesh wound.