Kurt Barlow was the main antagonist in Stephen King's second novel, 'Salem's Lot.
Role in The Dark Tower Series
Although Barlow never appears in The Dark Tower Series, he is mentioned various times specifically by Pere Callahan.
When explaining his story to Roland's ka-tet he tells them about the confrontation he had in the house of a boy named Mark. When Callahan's faith fails before Barlow, Barlow forces Callahan to drink from his neck, his blood. Callahan later reveals that he was cursed and left 'Salem's Lot, but Mark and Ben Mears were able to defeat Barlow.
When explaining the concept of vampires, Callahan tells Roland that Kurt Barlow is what he calls a "Type One" Vampire.