Who is James Calver from The Power and the Glory and what is their importance?

Calver is the wanted American referred to as 'the Yankee.' He robbed a bank in the United States and killed two federal agents. He escaped to Mexico and is on the run. His picture is on the wall of the police station along with the Priests. Towards the end of the story he is nearly caught and takes an Indian boy hostage, both of them are shot and the boy is killed. At the end of the story the man is dying and the priest is lured back to hear his confession. He tries to save the priest and feels guilty for helping the priest get caught. It is implied that he also killed another character in the story, Coral.