Transformer Optimus Prime now Western Star truck.

The famous action hero has changed form for the fourth Transformers movie directed by Michael Bay, now based on a new truck that is under development.

Children of the 1980s might recall the original Optimus Prime was based on a cab-over Kenworth, the K100. That version of the Autobot leader, was available in a toy that could change from a robot into a model truck and starred in the original cartoon series.

He then switched to a classic Peterbilt 379, a classic American rig with a super-long bonnet and upright nose that hurts fuel economy but looks cool, for the first Transformers films.

Now, Bay has revealed Optimus Prime has switched to a futuristic Western Star model with a more modern look.

Western Star, now owned by the giant Daimler group, has been involved in the process, although it’s not clear what kind of commercial deal was done between it and the producer.

Daimler released a statement confirming its involvement. “Daimler Trucks North America is excited to collaborate with Paramount on Michael Bay’s forthcoming Transformers 4,” it says.

The company says the Optimus Prime character will not be limited to the big screen. “This movie will feature a new truck now in development from Western Star that showcases the next level of innovation in the trucking industry,” the statement says.

Daimler provides no more details, except to say the new production Western Star truck that Optimus Prime is based on will be revealed next year. The production version of the truck won’t be an exact replica of the movie star model given it features a massive bonnet bulge that would dramatically reduce visibility and triple vertical exhaust stacks that point out to the side of the truck at the top of the cab.