Callahan is the "damned" priest who first appeared in the novel 'Salem's Lot. He makes his first appearance in the Dark Tower series in Wolves of the Calla, although his involvement in the series was hinted at in the afterword to Wizard and Glass. After being infected by the vampire Barlow, Father Callahan spends time in a homeless shelter that he later runs. Callahan made it a goal to get even with the vampires for what they did to his partner. He is aided in this due to his ability to spot the vampires; since Jerusalem's Lot (and the forced taking of some of the vampire Barlow's blood) he has been able to tell who is a vampire. He enters Mid-World after jumping from a window escaping the agents of the Red King, then arrives at the Way Station from the The Gunslinger (right after Jake & Roland left). He assists the ka-tet (becoming a partial member) in the Battle against the Wolves, helps Susannah's rescue mission from 1999 New York, sacrificing himself so that Jake may live, and making his final stand in The Dark Tower VII against the can-toi (low men) and vampires. Callahan kills himself before allowing himself to fall at the hands of the vampires in the Dixie Pig.