Weaver also acted in motion pictures, generally as a supporting player. He appeared in such movies as "Fail-Safe" (1964; as a jingoist and increasingly unstable U.S. Air Force colonel, ashamed of his foreign-born and alcoholic parents, whom he refers to as "those people"), "Marathon Man" (1976; as a professor advising the protagonist, a graduate student), "Black Sunday" (1977; as the lead FBI agent in an anti-terrorism effort) and "Creepshow" (1982); as a scientist who discovers a monster in a crate, and John McTiernan's remake of "The Thomas Crown Affair" (1999). He also had roles in "The Day of the Dolphin" (1973), "Demon Seed" (1977), "The Big Fix" (1978), and Sidney Lumet's "Power" (1986). Beginning in 1995, Weaver worked primarily as a voice actor, providing narration for programs on the History Channel. After making his third guest appearance on "Law & Order" in 2005, Weaver made a "secret decision to retire".