Here's how Gemini Man brought back 23-year-old Will Smith

At 23, Will Smith was a Grammy-winning rapper and star of his own hit TV show. Now, 28 years later, the world will once again be watching 23-year-old Smith — and seeing double.

The idea for Gemini Man has been kicking around for more than 20 years: Henry, a middle-aged assassin, battles his younger clone, Junior, who’s been sent to kill him. But technology had to catch up to finally bring the tale to the big screen, with Smith, 51, playing both characters in the Ang Lee-directed thriller.

The Aladdin star is just the latest A-lister to go back in time, after Samuel L. Jackson and Kurt Russell were recently digitally de-aged for Captain Marvel and Guardians of the Galaxy Vol. 2, respectively. But the Gemini Man team is quick to distance their film from any others.

“This is set to be the holy grail of visual effects — if we can do this,” Lee tells EW. “Scientifically, you know it can be done, but how we perceive it, that’s the leap of faith.” Lee worked with New Zealand-based Weta Digital to carry out his vision. “We took Will Smith and put in a full CGI creature, like the dinosaurs in Jurassic Park,” says Weta visual-effects supervisor Guy Williams (Avatar). “It’s not an augmentation, it’s a complete replacement.” To build this “digital creation,” Lee and his team combed through the actor’s life, with Bad Boys, Six Degrees of Separation, and, due to his military service, Smith’s own father serving as some of the best references for Junior.

Getting it right is crucial, says visual effects supervisor Bill Westenhofer (Wonder Woman), who also worked on the film: “If you get something that looks pretty close to real but isn’t quite there, it’s actually more disturbing than a completely caricatured version.” When it came to filming, Smith would play Henry opposite a stand-in, who served as an acting partner and reference for the special effects team. Then, for Junior, Smith would go into motion capture on a sound stage and act against the video of his Henry scenes.

The process was a bit simpler for Netflix’s Martin Scorsese-directed The Irishman (Nov. 1). Robert De Niro, Al Pacino, and Joe Pesci were able to portray their characters over a 40-year period thanks to a new camera and software system that translated their performances into 3-D computer-generated versions of their younger selves. But it wasn’t without its challenges. “Why I’m concerned,” Scorsese has said, “is that we’re so used to watching them as the older faces.”

Coming off of the Gemini Man experience, Smith has joked that he will now let himself go because he can just call in Junior for future movies. But what does this mean for movies moving forward? While Westenhofer thinks actors should “start banking themselves at different ages,” others worry about the process going too far. “I think there’s a limit,” says USC film professor Michael Fink. “There’s a point at which you’re essentially creating an animated character, and filmmakers need to think maybe that’s where they should stop.”

But we probably shouldn’t worry about a slippery slope just yet — for the most Hollywood reason of all: money. As Lee recently said: “I dare anyone to try. Junior is twice as expensive as Will Smith.”

Gemini Man, which also stars Clive Owen and Mary Elizabeth Winstead, opens in theaters on Oct. 11.

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