A Roman Catholic priest, Mulcahy was assigned as camp chaplain to the 4077th MASH
Mulcahy's job was to handle the spiritual care of not only the patients, but also the soldiers of the 4077. This was especially important when soldiers required the last rites or sacraments of the Catholic church, duties Mulcahy took very seriously and would not allow anyone to interfere with.
He's also a boxing fan, and boxer himself, despite being a pacifist.