The Birthday Party is a 1968 British drama film directed by William Friedkin, and starring Robert Shaw, based on the 1957 play The Birthday Party by Harold Pinter. The screenplay for the film was written by Pinter as well. The film, and the play, are considered examples of "comedy of menace", a genre associated with Pinter.
The film was a passion project for Friedkin, who had been a fan of the play, and he remained proud of the film after its release, though it was a box office disappointment.
(Summary from Wikipedia)