Who is Sergeant Fergus MacDonald from A Sparrow Falls and what is their importance?

Fergus MacDonald is an older man, slim of build and with feature reminiscent of a slum dweller. His eyes are set too close, and his lips are narrow, twisting down at the corners. Resembling a ferret, MacDonald's claim to fame is his association with the young crack shot, Mark Anders, whom he had the distinction of training. He has ginger hair and large freckles on his hands. Fergus is one of the ones intent on the new order of trade unions and Karl Marx.