Bowfinger

Bowfinger is a 1999 American comedy film directed by Frank Oz. It depicts a downandout filmmaker in Hollywood attempting to make a film on a small budget with a star who does not know that he is in the film. It was written by Steve Martin, and stars Martin, Eddie Murphy, and Heather Graham.

He manages to extract a promise from a film studio executive, Jerry Renfro, that the executive will distribute the film if it includes currentlyhot action star Kit Ramsey. Ramsey a rather pompous, neurotic, and paranoid actor refuses, so Bowfinger constructs a plan to covertly film on an extremely low budget all of Ramseys scenes without his knowledge. The actors, told that Ramsey is method acting and will not be interacting with them outside of their scenes, walk up to Ramsey in public and recite their lines while hidden cameras catch Ramseys confused reactions.The plan goes well at first Ramsey ends up starring unknowingly in the film. However, Ramsey who is a member of an organization called MindHead misinterprets the movies scifi dialogue and believes he is being stalked by aliens, damaging his alreadyprecarious mental state. He finally goes into hiding in order to maintain his sanity. This puts a hold on the film production, and leaves Bowfinger wondering what to do next. ........

Source: Wikipedia