How Michael Shannon and Kevin Spacey Became 'Elvis & Nixon’

— -- When Elvis Presley met President Richard Nixon in 1970, the photograph taken that day became the most requested image from the National Archives. Now, it has inspired the movie, “Elvis & Nixon.”

“One of the things that really drew me to the script actually is that even though this is ... based on a real event the meeting between them is completely mysterious ... there’s no documentation of it. There’s no recording of it,” Michael Shannon told ABC News’ Amy Robach in an interview for "Good Morning America."

Shannon, who plays “The King” opposite Kevin Spacey as Nixon, said preparing for the iconic role was a huge undertaking, and Spacey agrees. Merely mimicking Nixon like a glorified impressionist was something Spacey said he wanted to avoid.

"What I tried to do was just sort of find an essence of what was sort of Nixonian,” Spacey said. “And so I listened to a lot of tapes so that I could hear what he was like in private more than what he was like in public.”

Spacey said he discovered that Nixon “swore like a bat out of hell.”

Through his research, Shannon said he was surprised to learn Elvis was “deeply spiritual in nature.”

“I think a lot of times with the impersonations and what not, it leads you to a very superficial view of Elvis. He was actually a very deep thinker and he read a lot of books that I was surprised to find out that he was into,” Shannon explained.

The iconic Oval Office scene was the first place the actors’ saw one another in full wardrobe. While they managed to stay serious in the roles, there were lighter moments on set that cracked them both up.

“There were a couple of times when we were shooting and Michael would do something that was so brilliantly Elvis-like and I didn't expect it at all that I completely lost it,” Spacey recalled. “I think there were a couple times where I would do something that was very Nixon-like and he lost it, so there were a couple of times where we definitely lost it, but we tried very hard to keep a straight face.”

Spacey, who plays another president, Frank Underwood on “House of Cards,” hopes Underwood doesn’t come to mind during “Elvis & Nixon.”

"I hope that when people see me in an Oval Office set in this movie they won't think of Frank Underwood. And I hope when they see me as Frank Underwood they won't think of Nixon,” he joked.

“Elvis & Nixon” is in theaters now nationwide.