Optimus Prime appears in the "Transformers" live-action film series as the leader of the Autobots and one of the main protagonists. In the first three films, he is able to transform into a conventional Peterbilt 379 cab, rather than the cab over design of his original "Generation 1" body. In "", he gains a first generation-style trailer form before changing into a 2014 Western Star 5700 Concept. Also straying from the "G1" design, Prime's vehicle mode is now decorated with red flames painted onto a blue body à la Rodimus Prime, his "Generation 1" successor. The reason for the change was due to Director Michael Bay's decree that mass displacement does not occur when they transform, requiring Optimus's vehicle form to have more mass to achieve the desired size in his robot form.