J.K. Simmons seriously underwent a shred in order to play Commissioner Gordon in Justice League.

Aside from a tremendous amount of dedication to his regimen, Simmons credits part of his success to his trainer Aaron Williamson. An ex-Marine, Williamson's been providing elite-level training—morphing Hollywood A-listers into bona fide muscleheads like he's cranking out action figures on an assembly line—to the likes of Zac Efron, Dwayne Johnson, Jamie Foxx, and Jai Courtney. He first got his hands on Simmons in 2015 to help him shape up for Terminator Genisys.

At first, Simmons wanted to escape the doldrums of the film's set, which was based in Louisiana, but after shooting wrapped Simmons felt he was ready for a full-body change.

"He wanted to get into the best shape he had ever been in," Williamson says, adding, "J.K.'s goal was to adopt a healthy lifestyle and never have to worry again about health issues."