Leland Gaunt is the primary antagonist in Needful Things.
When he first appears in Castle Rock, Maine, Gaunt opens a shop called Needful Things. He seems like a charming man in his 50's or 60's. His eyes change color, depending on who is looking into them. His hands have no lines, and his index fingers are as long as his middle fingers.
Gaunt seems to have an unnatural awareness of the various relationships and rivalries throughout Caslte Rock, and his knowledge extends into knowing the most intimate material (and, in some cases, immaterial) desires of his customers. Throughout the course of the novel, Leland Gaunt is revealed to be a long-lived demon, bent on acquiring the souls of his unwitting customers.