Oscar-nominated special makeup effects artist and prosthetic designer Kazu Hiro details Johnson’s transformation into MMA artist Mark Kerr.

The Rock, who? How prosthetics helped Dwayne Johnson ‘completely disappear’ as Mark Kerr in The Smashing Machine

Oscar-nominated special makeup effects artist and prosthetic designer Kazu Hiro details Johnson's transformation into MMA artist Mark Kerr.

By Gerrad Hall

Gerrad Hall is an editorial director at **, overseeing movie, awards, and music coverage. He is also host of *The Awardist* podcast, and has cohosted EW's live Oscars, Emmys, SAG, and Grammys red carpet shows. He has appeared on *Good Morning America*, *The Talk*, *Access Hollywood*, *Extra!*, and other talk shows, delivering the latest news on pop culture and entertainment.

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December 4, 2025 11:00 a.m. ET

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Becoming the *Smashing Machine *required disguising the Rock.

"It was all-consuming," Dwayne Johnson, star of the biopic about MMA fighter Mark Kerr, tells ** of how big the challenge was not to be seen as his WWE persona on the big screen. "Because that was the goal: to completely disappear."

The actor knew where to turn for help with part of his physical transformation: special makeup effects artist and prosthetic designer Kazu Hiro. In total, Hiro designed some 22 prosthetics for Johnson — three-and-a-half hours to apply "eyes, nose, cauliflower ear, scars," the actor says (watch a timelapse of his transformation in the video above).

With credits also including *Looper*, *Salt*, *G.I. Joe: The Rise of Cobra*, *Angels & Demons*, *Norbit*, and *The Haunted Mansion*, Hiro says there's one aspect of this Benny Safdie-directed project that made it harder than all the others.

"Dwayne is so recognizable. No one looks like Dwayne, and he's so famous. Everybody knows what Dwayne looks like," he says. "So, without the destruction [to his face after fight scenes], it's about making him look believably like Mark Kerr. At the beginning, I was talking with Benny about how far we should take it likeness-wise, and our aim was to give an essence of Mark on Dwayne."

Dwayne Johnson and Emily Blunt in 'The Smashing Machine'.

Cheryl Dunn/A24

Oscar-nominated for 2023's *Maestro*, about iconic composer Leonard Bernstein and directed by and starring Bradley Cooper, his work also includes *Darkest Hour,* starring Gary Oldman as Winston Churchill, and *Bombshell*, where he transformed Charlize Theron into Megyn Kelly. With all of those biopics, like *Smashing Machine*, Hiro says he feels an obligation to respect the person being portrayed, especially if they are still alive, or if a surviving family member is perhaps participating in the production of the movie. But he also wants to honor the actor's face and the job they have to do.

"I cannot just pile up everything. The actor's emotion and the expression have to show through the prosthetic," he says. "If there's some element that is quite different compared to the original person and the actor, I cannot just keep adding stuff. So the important part is finding a good balance between functional and also practical.... I always try to design to keep it somewhere around two to three hours in the chair."

Fact-checking 'The Smashing Machine': MMA legend Mark Kerr compares the movie to his real-life story

Dwayne Johnson on disappearing into his 'Smashing Machine' role, Emily Blunt on the scene that made her vomit

But unlike those biopics, *The Smashing Machine* includes several fight scenes; Johnson is taking some punches, and so are those prosthetics.

"A challenging part was that the design, of course, has to have that likeness element, and also the makeup has to last a long time because of fighting and sweating and also abuse to the face," he says, laughing now about the complicated nature of the job. "So the makeup and also application have to be designed so it will last a long time."

After those fights, Kerr has injuries that require new prosthetics... on top of existing prosthetics, all of which can only be used once.

"The face, when they get hit, at first, they gradually start to swell. Right after a fight, [it's at its worst], and then it starts to heal," Hiro explains, noting that he watched the 2002 documentary *The Smashing Machine: The Life and Times of Extreme Fighter Mark Kerr* to study what would happen to Kerr's face and the different stages of healing.

Dwayne Johnson in 'The Smashing Machine'.

Hiro was one of 25-30 on the hair and makeup team; while he designed the prosthetics, Glen Griffin applied them; Oscar-winning hairstylist Mia Neal created Johnson's Mark Kerr wig, and others covered up Johnson's tattoos before painting on Kerr's.

***Check out more from EW's *The Awardist*, featuring exclusive interviews, analysis, and our podcast diving into all the highlights from the year's best in TV, movies, and more.***

"What I enjoy is that in that process, every day we build a trust, and I always enjoy the actor at the end, the actor seeing himself in the mirror," he says. "That process I really enjoy. And after all, we need a great actor to make our work work, to make it function."

Most actors will tell you they are their own worst critic — Hiro, it turns out, is his own, too.

"I'm never happy with my work," he says, laughing, after hearing what Johnson said about how crucial his work was to his transformation. "Whenever an actor shows up, everybody is so impressed, happy, so I'm like, okay, okay, it is maybe fine. I [rewatch] movies after five or six years and I realize, okay, that wasn't that bad. I think most of the great people I know, they're never happy about their work because there's always something to learn. That's how we progress and improve ourselves."********

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