1.
“You’re gonna need a bigger boat” from Jaws, another of cinema’s most quoted lines, was also an improvisation. The line had actually become a running joke during production, in reference to producers Richard Zanuck and David Brown being stingy. “It became a catchphrase for any time anything went wrong,” writer Carl Gottlieb said. Roy Scheider kept throwing it in during filming, and the one that made it in was the now-famous scene after his character first sees the shark.
2.
There was no dialogue written for the famous “You talking to me?” scene from Taxi Driver. Director Martin Scorsese asked Robert de Niro to just say something to himself in the mirror. “He kept saying, ‘You talkin’ to me?'” Scorsese continued. “He just kept repeating it, kept repeating it … It was like a jazz riff. Just like a solo.” De Niro said he had no idea how famous the line would become. “You never know with any of that stuff. You just did it.”
3.
In the opening scene of Batman, Michael Keaton was actually supposed to say “I am the knight” or “I am vengeance.” But he and director Tim Burton felt neither one worked — so Keaton improvised the now-iconic “I’m Batman.”
4.
The hilarious “she talks in her sleep” line in Indiana Jones and the Last Crusade was improvised by Sean Connery.
5.
Matthew McConaughey came up with what would become his own tagline as an actor: “alright, alright, alright.” He first uttered the phrase in Dazed and Confused, and got the idea from listening to a live recording of the Doors while in the car and hearing Jim Morrison say “alright alright alright alright” between tracks. McConaughey (who wasn’t even initially supposed to be in the scene) used each “alright” to represent one of the tenets of his character: rock and roll, getting high, and his car.
6.
Good Will Hunting’s memorable final line could’ve easily been something else. Robin Williams tried out dozens of different lines, but when he said “He stole my line,” writer and star Matt Damon knew it was perfect, thinking in the moment, “Holy shit, what a line, how did we not think of that?”
7.
One of the most famous lines from Casablanca — and, honestly, movie history — is “Here’s lookin’ at you, kid.” Humphrey Bogart himself actually came up with the line while filming the Paris flashbacks, and the writers decided to use it a few more times in the film — including in this iconic ending scene.
8.
One of the most quotable lines from Alien is “game over!” Bill Paxton actually came up with that line himself (though it was in rehearsals and not while they were filming). “‘Game over, man!’ was really the background of the character. I figured he was kind of the enlisted version of Gorman, who was the officer [played by] Bill Hope, who probably came up on video games. Back in those days, … at the end of your quarter, it would always be ‘Game over’ [on the screen]. So I wondered if anyone had ever used that [line], because it was kind of good. I had no idea it would catch on.”
9.
Jack Nicholson was meant to say “You already have the truth” in this scene from A Few Good Men. Instead, he ad-libbed “You can’t handle the truth!”, which became the most well-known line from the film.
10.
Nicholson also improvised the unhinged “Here’s Johnny!” from The Shining, as a reference to Johnny’s introduction in The Tonight Show Starring Johnny Carson. The line became so famous, it’s on t-shirts for the film.
11.
In Peter’s death scene in Avengers: Infinity War, director Joe Russo just told Tom Holland that Peter didn’t want to die, and Holland came up with the lines on his own. This includes the famous “Mr. Stark, I don’t feel so good” line that was so famous it literally became a meme.
12.
And in Avengers: Endgame, the famous line Morgan says to Tony that he later repeats back to her was originally “I love you tons.” Downey Jr. himself suggested Morgan change it to “I love you 3,000” as that’s something his real-life children say to him.
13.
Downey Jr. also came up with his famous “I am Iron Man” line at the end of Iron Man, which arguably changed the trajectory of the entire MCU.
14.
One more Marvel one: Dave Bautista improvised the hilarious “why is Gamora” line in Avengers: Infinity War, in the memorable scene where the Guardians meet Tony, Peter, and Dr. Strange.
15.
The “tears in rain” speech from Blade Runner was partly improvised. Actor Rutger Hauer was given a much longer speech to say, but he rewrote and improvised a shorter version. In particular, he came up with the “tears in rain” line, which is perhaps the most famous line from the entire film.
16.
The famous Midnight Cowboy scene where Rico slams his hands down on a taxi that almost hits him and yells “I’m walking here!” was an improvisation. They didn’t have the money to create a full set with extras, so they used a “stolen shot” — using a hidden camera on a real street. At one point the characters cross the street — they had rehearsed and timed the dialogue so they could cross when the signal was green. But in the first shot, a car ran the light and almost hit them. Staying in character, Dustin Hoffman yelled, “I’m walking here!” Today, it’s one of the most quoted movie lines of all time.
17.
Billy Crystal improvised the oft-quoted part in When Harry Met Sally when he talks about pecan pie in a silly voice. Meg Ryan went with it — but not before laughing and looking off-camera, which you can see in the final scene.
18.
Two memorable lines from Harry Potter and the Chamber of Secrets were improvised: first, Lucius’ comment about Harry always being around to play the hero, as well as Harry’s retort that he will be. Jason Isaacs and Daniel Radcliffe came up with those lines on the spot. Isaacs called Harry’s reply his favorite line in the franchise.
19.
Malfoy’s funny line, “I didn’t know you could read,” was also an ad-lib from Tom Felton — he’d forgotten his real line.
20.
While Gerard Butler didn’t improvise the iconic line “THIS IS SPARTA” in 300, his shouting of the line was just a throwaway last take. “I had done quite a few takes and most of them were ‘This is Sparta,’” Gerard told the Hollywood Reporter, saying the words in a low growl. “And it’s part process and part insecurity, maybe. And I go, ‘Can I just try another?’” The actors in the crowd actually stifled laughter at his over-the-top delivery, but director Zack Snyder loved it. The screaming is what made the line so famous and imitated.
And finally, let’s end on two that the actors didn’t come up with themselves, but were still suggested (by others on set) in the moment:
21.
In A Quiet Place, John Krasinski’s character was just supposed to say “I love you” before he died. Millicent Simmonds suggested he say “I have always loved you” instead, and he went with it on set. The devastating moment was one of the most memorable from the film.
22.
The classic “What are you waiting for?” line in I Know What You Did Last Summer was suggested and directed by a child who’d won a contest to create a moment in the film.
23.
And finally, the incredible “He’s a friend from work” line in Thor: Ragnarok was suggested by a kid — a Make-a-Wish recipient who was visiting the set.
