Downey was added in order for the film to adapt the 2006–07 "Civil War" comic book storyline written by Mark Millar, which pitted Iron Man against Captain America.
Downey ditambahkan agar film tersebut dapat menyesuaikan alur cerita komik buku komik 2006-07 "yang ditulis oleh Mark Millar, yang mengadu Iron Man melawan Captain America.