Robert Downey Jr. played a big part in laying the foundation for the MCU when he improvised the line "I am Iron Man" as Tony Stark at the end of the 2008 film.

Stark repeated a version of the line several times in the franchise, but other heroes also made their own versions of the announcement when introducing themselves to the MCU.

The first time Elaine shouted "Get out!" and literally shoved the person who delivered the exciting or shocking news was improvised by Julia Louis-Dreyfus.

This improv was based on the fact that she did something similar in real life. The audience loved it, and it became one of the funniest, longest-running Elaine gags on “Seinfeld.”

During the rehearsal for Ross and Emily’s wedding scene, David Schwimmer accidentally flubbed the line and said "Rachel" instead of "Emily.”

While it wasn't technically an ad-lib, it was an unplanned moment that got such a big reaction the writers added it to the script and worked it into the show’s plot.

In Kelvin Timeline of the 2009 film, Dr. McCoy (Karl Urban), while explaining his divorce to Captain Kirk (Chis Pine), states, "All I got left is my bones."

Director J.J. Abrams confirmed that Urban ad-libbed the hilarious line, which — for the Kelvin Timeline at least — is the canonical reason Kirk started calling McCoy "Bones."

While filming the scene where Michelle and Jim finally hook up, Alyson Hannigan decided to take Michelle to an even raunchier level by ad-libbing, "Say my name!.”

The producers were initially iffy about keeping the line, but Hannigan talked them into it. Michelle's dominant side became a key aspect of her character for the rest of the films.