Father Donald Frank Callahan is a fictional character created by Stephen King. He originally appeared in the 1975 novel 'Salem's Lot and later The Dark Tower, appearing in The Dark Tower V: Wolves of the Calla, The Dark Tower VI: Song of Susannah and finally The Dark Tower. He is at first an alcoholic with a troubled faith, but he seems to find his peace in The Dark Tower novels, and his faith is restored.

'Salem's Lot is a 1975 horror novel by American author Stephen King. It was his second published novel. The story involves a writer named Ben Mears who returns to the town of Jerusalem's Lot in Maine, where he lived from the age of five through nine, only to discover that the residents are becoming vampires. The town is revisited in the short stories "Jerusalem's Lot" and "One for the Road", both from King's story collection Night Shift (1978). The novel was nominated for the World Fantasy Award in 1976 and the Locus Award for the All-Time Best Fantasy Novel in 1987.