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. Callahan failed in his confrontation with the vampire Barlow in Salem's Lot and spent years wandering before finding purpose again with Roland's ka-tet. His backstory occupies a substantial section of Wolves of the Calla. He dies in Song of Susannah rather than be taken by the Crimson King's forces, choosing his own end.