A former Catholic priest first introduced in King's Salem's Lot, who crosses into the Dark Tower universe and eventually settles in Calla Bryn Sturgis. Whatever happened to Callahan in his New England parish - and the answer is not the kind of thing a man can give a short version of - left him spending years wandering before finding purpose again with Roland's ka-tet. His backstory occupies a substantial section of Wolves of the Calla.