Who is Captain Harold Sells from The Killing Zone: My Life in the Vietnam War and what is their importance?

Captain Sells is the immediate superior officer of Lt. Downs and leads the Delta Company, a force of 3 or 4 platoons, or around 100 men. He is a career military man, who has served about 9 years in the Army. Captain Sells is concerned about Fred Downs after Downs is slightly wounded twice in one day in a bloody battle. He is willing to allow Lt. Downs to leave the field and get a safe job in intelligence, but ultimately Lt. Downs decides he cannot abandon his men. Captain Sells also has certain hesitations about killing civilians and at least once overrules Lt. Downs to release a captured civilian. In the Afterword, it is mentioned that Captain Sells leaves the Army after he survives his tour of duty in Vietnam.