Robert Downey Jr and director Jon Favreau had to heavily improvise the dialogue for the first Iron Man movie in 2008 because they began filming without a completed script.

A closer look

Robert Downey Jr and director Jon Favreau had to heavily improvise the dialogue for the first Iron Man movie in 2008 because they began filming without a completed script. The studio was far more focused on getting the action sequences right than actually figuring out what the characters were supposed to say to each other. Jeff Bridges essentially treated the massive blockbuster like a wildly expensive student film, noting that they would just gather in a trailer before shooting to figure out the scenes on the fly. It perfectly summarizes the absolute chaotic absurdity of the Hollywood machine that the foundational movie of the multi-billion-dollar Marvel Cinematic Universe was basically just highly paid actors doing improv comedy in expensive metal suits while executives crossed their fingers