9. John Belushi as John “Bluto” Blutarsky in Animal House
Director John Landis gave Belushi a cafeteria full of actors and no direction. Landis apparently knew comedy gold was about to be forged, though, because he did urge the cameraman to “stay with him” while Belushi was filling his tray.
8. Peter Sellers as Dr. Strangelove in Dr. Strangelove or: How I Learned to Stop Worrying and Love the Bomb
Perhaps chalk it up to playing three different roles in the same film, but Sellers forgot Dr. Strangelove was wheelchair-bound and made up these lines the second he recognized his mistake.
6. Robin Williams as Genie in Aladdin
Williams’s 16 hours of improv included 14 impressions and a Scottish accent — the one he’d famously use the following year in Mrs. Doubtfire — that cost this movie an Academy Award nomination for Best Adapted Screenplay.
1. Robert De Niro as Travis Bickle in Taxi Driver
The script for this scene only had the words, “Travis looks in the mirror,” so De Niro, inspired by a Brando flick and using an actor’s technique to practice lines, made up every part of this scene.