Who is Colonel Charles Harris from A Test of Wills and what is their importance?

The book begins with Colonel Harris's murder. He is shot at near point blank range, while mounted on his horse. The narrator says that he dies hard with a roar of displeasure. In the course of his investigation, Rutledge is frustrated by the fact that Colonel Harris seems to have only one enemy in the village, and that man, Mavers, has a near air-tight alibi. Colonel Harris is survived by his ward, Lettice Wood, and no other family. He served honorably in two wars, and by all accounts was a charismatic, thoughtful, vigorous man.