Michael Keaton is often credited with creating the iconic “I’m Batman” line from Tim Burton’s 1989 film. However, director Jon Peters claimed in a documentary that the original line was “I’m Batman, motherf–ker.” Although Peters has a history of questionable concepts for DC Comics adaptations, most accounts suggest that Keaton came up with the line on the spot, without the vulgar language.
The famous line took Keaton’s performance to new heights, showcasing his ability to convey the character’s intensity and determination. It has since become a defining moment in Batman’s cinematic legacy and has been referenced and reinterpreted in various projects, including Batman: The Animated Series and Batman Begins.
In addition to its impact on Kevin Conroy’s portrayal of Batman, the line has also influenced subsequent actors’ interpretations of the character. Christian Bale and Robert Pattinson have both used variations of the phrase, while Terry McGinnis (voiced by Kevin Conroy) famously repeated it in Batman Beyond.
Source: https://www.cbr.com/most-famous-line-in-batman-movie-history-not-scripted