“But not at all in a real way.

It’s a very different story, but one that does overlap.”

Cash was not originally a part ofA Complete Unknown(in theaters Christmas Day).

Boyd Holbrook as Johnny Cash in A Complete Unknown

Boyd Holbrook as Johnny Cash in ‘A Complete Unknown’.Searchlight Pictures

“The Johnny Cash part wasn’t in [the book]Going Electric,” Holbrook explains.

He didn’t know that when he madeWalk the Line."

Dylan shared the letters with Mangold, who lifted some of the film’s dialogue directly from them.

Boyd Holbrook as Johnny Cash in A Complete Unknown

Boyd Holbrook in ‘A Complete Unknown’.Searchlight Pictures

“It’s a beautiful series of letters,” adds Mangold.

“Johnny started writing to Bob after hisFreewheelin’album came out.”

Holbrook was also able to read and use the letters to inform his performance.

Boyd Holbrook as Johnny Cash in A COMPLETE UNKNOWN

Boyd Holbrook in ‘A Complete Unknown’.Searchlight Pictures

“He found them through Bob.

That really tells you which person is which.

I read those and they’re great, man.

johnny cash portrait

Johnny Cash in 1969.Image courtesy of Getty Images / The Hulton Archive

They’re on the back of airplane sickness bags.

These guys are at the pinnacle of their lives, road dogs traveling in the isolation of maximum fame.

They’re a big insight into them and their lives and what made them tick.”

Johnny Cash and June Carter, Walk the Line

Reese Witherspoon and Joaquin Phoenix in ‘Walk the Line’.Suzanne Tenner/20th Century Fox

Still, Holbrook was initially apprehensive about playing such an iconic musician.

“I said, ‘Well, I don’t look anything like Johnny Cash.’

And he said, ‘Well, nobody looks like anybody really.’

Boyd Holbrook as Johnny Cash in A Complete Unknown

Boyd Holbrook in ‘A Complete Unknown’.Searchlight Pictures

Nobody does, but you might build in these impressions and this essence.”

And it was added value to Holbrook that Mangold knew Cash’s story so well.

“Johnny’s purpose in this story had nothing to do with that movie,” the actor notes.

Edward Norton and Timothée Chalamet in A COMPLETE UNKNOWN

Edward Norton as Pete Seeger and Timothée Chalamet as Bob Dylan in ‘A Complete Unknown.'.Macall Polay/Searchlight Pictures

“Yes, Jim made that movie.

But I wouldn’t have done this if somebody else had asked me to do it.”

“That’s brimming out of me and of my own sense of humor.

That’s pretty rough.

“Bob is not that story.

If anything, he’s kind of a mystery.

No one can ever quite figure out who is he.

He is so many people all in one.

“John was 35-ish and Bob was probably early 20s,” notes Holbrook.

“Johnny reached out to him saying how brilliant his music was.

So, you had the older guy extending his hand to the younger one.

There’s a humility in that, and there’s an admiration of Bob too.

But Bob is a sponge in a sense.

Because if you’re not careful, the machine will eat you alive.”

“Maybe they’re comrades.

Macall Polay/Searchlight Pictures

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“It’s not just a history lesson about music,” the director says.

“It’s really about this unique character.

Why are some people so special and how does that affect them?