Cullen recalls auditioning for the role of the robot superhero Optimus Prime at a casting house in Burbank, California, explaining that as he read Prime's character breakdown, he saw that it was "the opportunity of the year", and heeded his brother Larry's advice: "Peter, don't be a Hollywood superhero, be a real superhero. Real superheroes don't yell and act tough; they are tough enough to be gentle, so control yourself." Cullen later learned from his agent, Steve Tisherman, that he not only won the part of Prime, but also, to his surprise, the role of Ironhide as well, which he saw as a "home run".