Haley will play Sayre, a menacing humanoid who is the vampire leader and kowtows to no one.
Here is a description of Sayre from The Dark Tower WiKi.
Richard Patrick Sayre is a high-ranking can-toi and a member of the Sombra Corporation. He has the usual low man fashion sense, dressing himself in a garish suit. He also has the pool of blood on his forehead that never spills over.
As revealed in Wolves of the Calla, Sayre lured Father Callahan to Sombra's offices by offering a million dollars to the charity he was working for. It was a trap, where Sayre intended to use Type Three vampires to give Callahan AIDS. His plan failed when Callahan committed suicide by jumping out the window.
In Song of Susannah and The Dark Tower, Sayre is the man in charge of delivering Mia's baby. He calls Susannah/Mia in their hotel room, telling them to go to the Dixie Pig. He takes them through the door into Fedic, where Mia is placed on a bed to deliver Mordred Deschain. After his birth, Susannah grabs a gun and shoots Sayre in the head.