Who is Harry Callaghan from See How They Run and what is their importance?

Harry Callaghan is an FBI agent who has sacrificed his best years in the service of his country. Determined, and dedicated to his position, he has lost most everything else in life in order to be the best at his job. His wife Betsy had been a great sacrifice to the job, as had his son Martin who was now a senior at Pitt, but he had the satisfaction of being 'a good investigator' the director had told him. The director had correctly realized that this kind of praise would drive a man like Harry Callaghan harder and further than any amount of criticism would. Callaghan forces himself to stay focused on the job at hand, and consoles himself with the fact that there is something special about David and Alix. There was something about the two of them together that made them worthy of front-page news from the start.