In director Ang Lee’s new movie, Gemini Man, retired assassin Will Smith is hunted by his younger self. 2019 PARAMOUNT PICTURES. ALL RIGHTS RESERVED

The young Will Smith of Gemini Man is not the fresh Prince you probably remember. He is physically bulkier, having been raised in a militaristic household by a shadowy character played by Clive Owen. Also, he lacks the signature mustache—the discussions over that decision were “intense,” Westenhofer says. And Smith is now a better, more serious actor than the kid in the fluorescent cap who jeered “Smell ya later!”

In an interview, the human Will Smith seems to be, if anything, invigorated by the passage of time. “Man,” he tells me, “life is delicious.” He was intrigued that the behind-the-scenes process of making Gemini Man mirrored the cloning plotline of the film itself. “I've always loved science fiction, and what's really interesting on this one is that there's a certain amount of science fiction within the film becoming science fact outside of it,” Smith says. “The guys are actually doing it.”

Back in early 2018, Weta scanned Smith with an array of high-resolution cameras while he performed a predetermined set of facial calisthenics, compiling a vast database of the full expressive repertoire of Smith's face. A model of Smith's body was fitted with a core digital skeleton and muscle system, the biomechanical chassis Weta uses for nearly all of its computer-generated humanoids, creating a basic digital replica—or clone, if you will—of modern-day Will Smith. In the primordial nothingness of Weta's hard drives, Junior was born. The next task: reverse-engineer by hand that digital 49-year-old into the shape and form of a 23-year-old.

For visual reference, the team amassed stills and clips of early- to mid-'90s Will Smith. Bad Boys, Six Degrees of Separation, and, of course, later episodes of Fresh Prince of Bel-Air were pored over like sacred texts. The team unsentimentally scrutinized old childhood photographs and even sourced a relatively crude facial cast of the actor that came from Independence Day.

Around mid-2018, the team tried an experiment they called the Pepsi Challenge, dropping the Junior-in-progress into the middle of a scene from Bad Boys, which was made in 1995, and animating it manually. It was a little wobbly, but it convinced them they were on the right track.

Throughout the rest of 2018, Junior continued to evolve into something resembling fleshy, organic life, one facial and bodily component at a time. One team modeled Smith's teeth—not only the enamel on the outside but the dentin on the inside—while another worked on the way the lips compress. They mapped out the pores, so that the skin creased and wrinkled along its natural fault lines. They studied the balance of the pigments of the skin and the particular way black skin refracts light at a subsurface level. They even chiseled away at the skull. And they spent a lot of time gazing deeply into Smith's eyes: the sclera, the cornea, the inky film on the inside of the eye called the choroid. They modeled how the cornea interacts with the iris and how the iris interacts with the pupil. They modeled the conjunctiva, the thin transparent membrane that envelops the surface of the eye. Then there was an ocular breakthrough. “We've always done a relatively spherical eye,” says Guy Williams, one of the heads of the Junior team at Weta, who reports to Westenhofer. “We realized that a real eye, when it's sitting inside the socket, is actually squished into shape.” So, yes, they proceeded to squish Will Smith's eyes.

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The team at Weta was building on its own extensive research on the dynamics of skin, blood flow, breathing, and more, which the effects artists largely taught themselves. “God knows we're not saving lives here or anything like that,” Williams says. “But you have to treat it almost like medicine. You have to be clinical and objective about it.” Cold dispassion meant representing Smith's face honestly in its human imperfection, however slight. “If he has a quirk about his face—and I won't go into those out of respect—you have to have that in there.” (Look out for Smith's one misaligned mandibular lateral incisor, dutifully replicated in CG.) As the months wore on, Williams says, the refinements and adjustments became comically pedantic. “There are times in this job where you have a roomful of mature, middle-aged people sitting around a monitor, looking at a screen, talking about the amount of shine a pimple should have.”