Did Robert Downey Jr. really improvise the line that changed the MCU forever?

The answer

The original Iron Man script ended with Tony Stark following the standard superhero playbook and denying his identity at a press conference. But Robert Downey Jr. went off-script and blurted out 'I am Iron Man,' stunning the crew. Producer Kevin Feige kept the take because it perfectly captured the character's comic book personality. That single ad-lib fundamentally altered the MCU's trajectory by abolishing secret identities across the franchise. Feige later said the moment taught Marvel that their films should be 'inspired by the comics rather than slavishly devoted to them,' setting the creative philosophy for the entire Infinity Saga.