Turns out, if you stare at Arnold Schwarzenegger long enough, you begin to notice that he has a slight bow in his nose and that his face, like most of ours, is asymmetrical, especially when he makes an expression. “One eye is always a bit wider than the other,” says Sheldon Stopsack, a visual-effects supervisor tasked with creating this summer’s flat-out wildest action scene. In Terminator Genisys, Schwarzenegger’s time-traveling robot assassin battles no less a foe than… his younger self. “The greatest compliment we could get is if people think we reused footage from the 1984 movie,” says producer David Ellison.

They didn’t. James Cameron’s original 1984 TheTerminator includes an early scene that has become a sci-fi touchstone: A naked man (Schwarzenegger) arrives in a flash of lightning and smoke at the Griffith Observatory in Los Angeles, takes on three punk rockers who harass him, and steals their clothes. ForGenisys, the filmmakers re-created that scene, but with a pivotal twist. This time, the Terminator shows up in the same spot in the ’80s, on a mission to eradicate Sarah Connor (Game of Thrones’ Emilia Clarke), but runs into his older self—a now heroic cyborg who has become a father figure to Sarah. The old and young Terminators, 30 years apart in age, then tangle in an epic matchup while the punks look on. Schwarzenegger, 67, loves the scene. “I think it’s very smart to use my age in this way,” he says. “It’s very well-thought-out.”

It kind of had to be, because that one scene required an entire team to design and create a fully digital, photo-real Schwarzenegger, something that had never been done this extensively on screen with a living actor. When Stopsack, who has worked onGuardians of the Galaxy and X-Men: Days of Future Past, first heard the idea of creating a synthetic actor—or “synthespian”—he was equal parts excited and terrified. “It’s a completely crazy idea due to the sheer complexity of the task,” he says. “To work on a digital human being is considered the holy grail in visual effects.”

The ambitious digital trickery required Stopsack’s team of animators and designers at MPC to labor for 12 tension-filled months to create 35 shots that fill a mere five minutes of screen time. 

Stopsack and the film’s VFX super-visor Janek Sirrs had to search through practically every piece of archival footage ever shot of Schwarz-enegger (yes, even Kindergarten Cop) and take a deep dive into his 1977 documentary Pumping Iron (see below). “I think they’ve looked at more photographs of Arnold Schwarzenegger than any two people on the planet,” says Ellison. The sequence was fine-tuned until the very last second—it was completed just 30 minutes before the final print was submitted to the studio. “It was down to the wire,” Ellison says. 

How’d they do it? See the step-by-step process below.

Step 1: Find the Right Body Double

The production scoured the globe for a man with a 50-inch back who could double for a young Schwarzenegger. They found their guy in 27-year-old Brett Azar, an Australian bodybuilder. “Brett was the only one who matched those specifications,” says Ellison. “It turns out Arnold was his idol.” On set, Azar faced off against Schwarzenegger in the fight scene between the two Terminators. Then the special-effects team got involved.

Image Credit: Everett Collection

Step 2: Build the Digital Face

Every detail of Schwarzenegger’s face was stored in a vast library of images that animators used to create the actor’s younger face. The technicians also conducted a performance-capture session with Schwarzenegger to record his present-day features. “We took the results from this facial-capture session and tried to map that onto our younger build and compensate for the discrepancy between the ages,” says Stopsack.

Step 3: Perfect the Body Language

The multidimensional shots of Schwarzenegger’s physique captured in the 1977 documentary Pumping Iron became crucial pieces of information while building the young Arnold—helping to re-create everything from his pecs to his glutes. “Arnold’s body is so unique, we really had to deviate from the [body double],” Stopsack says. “We digitally replaced Brett for the majority of the shots in favor of creating realism and believability.”