15. Al Jolson as Jackie Rabinowitz in The Jazz Singer
The opening lines that were America’s introduction to audible dialogue in a feature-length film were completely ad-libbed.
14. Ryan Gosling as Jacob Palmer in Crazy, Stupid, Love.
Though Gosling only does it with his friends while out, his suggestion to do the final move from Dirty Dancing made its way into the final cut.
13. David Patrick Kelly as Luther in The Warriors
Kelly was haunted by a neighbor who used a similar sing-song to taunt him, which led to him both making up this line and delivering it so terrifyingly.
12. Bill Paxton as Pvt. Hudson in Aliens
While claiming to improvise the majority of his lines in this movie, this is far and away Paxton’s best piece of ad-libbed excellence.
11. Orson Welles as Harry Lime in The Third Man
Welles ad-libbed an entire speech that was in neither the book nor the script and turned it into the most-quoted bit from the whole movie.
10. Humphrey Bogart as Rick Blaine in Casablanca
Bogey had uttered the line in a different movie, but it didn’t land until he decided to add it to this one.
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.
7. Bill Murray as Carl Spackler in Caddyshack
Harold Ramis told Murray to narrate himself while golfing, so he made up every line of dialogue in the scene on the spot.
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.
5. Richard Castellano as Clemenza in The Godfather
Clemenza telling Rocco to “Leave the gun” after killing Paulie was in the script, but then Castellano doubled down with one of the most gangster lines of all time.
4. Roy Scheider as Brody in Jaws
A true testament to Scheider’s acting ability, he deadpanned this classic without any prompting from anyone.
3. Harrison Ford as Han Solo in Star Wars Episode V — The Empire Strikes Back
The script called for “Just remember that, Leia, because I’ll be back” as a response to Leia’s “I love you,” but we got this infinitely cooler gem instead.
2. Joe Pesci as Tommy DeVito in Goodfellas
Scorsese let Liotta and Pesci improvise the entire tense scene in order to get real reactions from all the actors surrounding them.
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.