Ezra Miller stars as Barry Allen aka The Flash in the new DC Extended Universe movie Justice League.
Miller has revealed he was encouraged to react to his co-stars and come up with many of his own lines and movements.
Miller and his Flash are the comic of the superhero squad.
Speaking at the film's world premiere Miller said "There was a lot of improv. I improvised every day, on every scene."
He went on to say "It was just a good way to work with this character and thankfully I was allowed to do it."
Justice League hits theaters Friday, November 17th.