Who is Lord William Pumphrey from Sharpe's Prey: Richard Sharpe and the Expedition to Copenhagen, 1807 and what is their importance?

Lord Pumphrey is a protector of Britain, described as something of a sociopath and ruthless in his pursuit of ridding his country of threats. Pumphrey is a former schoolmate of Lavisser's from Eton, and a man Sharpe finds completely likeable.