Answer
Lankester Merrin was a character played by Max von Sydow in the 1973 horror film The Exorcist. Merrin was a retired Jesuit priest who was called in to help with the exorcism of a young girl, Regan MacNeil, who was possessed by a demon. Merrin was a wise and experienced exorcist, and he was able to defeat the demon and save Regan's life.