Elvis "can't be an impersonation – it's got to be an interpretation"

"There's a line in the movie – 'When I first saw Elvis in the 50s, I cannot overstate how strange he looked, and how shocking he was,'" he said.

"Now, here's our job. How do we translate strange and shocking to a contemporary audience? So to a certain degree, there are things we absolutely went apples to apples with. I'd like to think he'd go 'Gee, that's exactly like it was in the '68 Comeback special,' right? Because it's in the modern era.

"But there are other things where it can't be an impersonation – it's got to be an interpretation. Because we don't have the source material, and even if we did, it's filtered through old nostalgic technology. So Austin's number one mission, from the moment I met him, was to humanise Elvis Presley, was to show the person and the journey."

For his part, Butler says that when he was first cast, he spent a lot of time trying to perfect Elvis's voice – before ultimately realising that finding "the humanity and the life within" was of greater importance.

"When I began the process of this, I set out to get my voice to sound identical to his," the actor said. "That was sort of my goal – if you heard a recording of me and you heard a recording of him, you wouldn't be able to tell the difference. And I held that for a long time.

"And so what that does is it also instills fear, you know, this fear that I'm not going to achieve that or whatever. And so that got the fire burning inside me to work, and work and work, and so maybe a year before we even started shooting I was doing six, seven days a week of voice coaching and working with different experts and just trying to get the register to be in the right place, and the dialect and the way he inflects and everything.

"But ultimately, the life is important, is what we sort of realised. You can impersonate somebody, but to find the humanity and the life within and the passion and the heart, ultimately I had to release myself from the constraints of that and try to live his life as truthfully as possible."

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