Who is Father Donald Callahan from 'Salem's Lot and what is their importance?

Fifty-three-year-old, Father Callaghan, is the priest at St. Andrews. He is described as a handsome man, with a quick smile. Unfortunately, Father Callaghan has a drinking problem that interferes with the good he can do within in his parish. When he fights against evil (Barlow), the priest loses. He does, however, have the strength to leave town and what would eventually be Barlow's control.