Inside Donald Trump's relationship with Rev. Billy Graham

— -- One of the most influential figures in American religious life, Rev. Billy Graham preached to the masses but also exerted unofficial spiritual influence on numerous U.S. presidents, including Donald Trump.

While President Trump never met with Graham during his first year in office, he celebrated with Graham at his 95th birthday party in 2013 and spoke regularly of his towering example of faith from the campaign trail in 2016.

Graham died Feb. 21 in his sleep at his North Carolina home, his spokesman said at the time. He was 99.

On Friday, President Trump and First Lady Melania will travel with Vice President Mike Pence and Second Lady Karen Pence to Charlotte, North Carolina for Graham’s funeral. Trump will be the only living president to attend.

Trump has said his fondness for Graham, known as "America's Pastor," stems from his protestant father, Fred Trump.

"It's a relationship that goes back to his childhood," David Brody, the author of "The Faith of Donald J. Trump: A Spiritual Journey," told ABC News. "Trump has an affection for Billy Graham based on the fact that his father loved Billy Graham."

This week Trump, who rarely speaks publicly of his upbringing, recalled during a memorial service for Graham at the U.S. Capitol how his father spoke admiringly about Graham's famous evangelical revivals or so-called crusades, held in New York City.

"My father said to me, 'Come on, son' -- and, by the way, he said, 'Come on, mom. Let's go see Billy Graham at Yankee Stadium.' And it was something very special," Trump recalled Wednesday.

Graham preached at hundreds of revivals around the world from the 1950s up until his retirement in 2005.

"Americans came in droves to hear that great young preacher, Trump said. "Fred Trump was a big fan. Fred Trump was my father."

The Trump connection to the Graham family has grown deeper with his foray into politics.

The president has enjoyed a strong backing from the Graham family, receiving their endorsement during his campaign and while in office. Rev. Graham's son Franklin -- president and CEO of the Billy Graham Evangelistic Association and the international charity Samaritan's Purse -- has been a prominent booster and defender of the president

"The world is attacking Christians because they hate the name of Christ," Graham told Fox News last month. "And President Trump has been defending Christians. I find this refreshing to have a president who’s not afraid to say Jesus, he’s not afraid to have prayers where people end in the name of Jesus.

"We’ve never had this, not in my lifetime, and he defends the Christian faith more than any president in my lifetime," he said.

Tony Perkins, president of the conservative Family Research Council, has traveled together with Trump and Franklin Graham, and told ABC News that Trump admires the Graham family.

"He has a close relationship with Franklin who has been helpful to him, and he appreciates the leadership President Trump has brought," Perkins said. "He’s spoken out on the President's behalf, but I think he’s also been helpful spiritually."

But some in the Christian community have found the Graham family's embrace of Trump surprising, given the president's documented record of profanity, harsh rhetoric toward immigrants and minorities, sexual assault allegations, and reports of alleged of marital infidelity.

New York megachurch pastor A.R. Bernard quit the White House’s evangelical advisory board over Trump’s response to violent protests in Charlottesville. "It became obvious that there was a deepening conflict in values between myself and the administration," Bernard said in a statement.

In the wake of Trump reportedly calling certain African countries "s---holes" during an Oval Office meeting in January -- comments which Trump disputes he said -- Rev. Graham’s own granddaughter Jerushah Armfield said Trump should ask for public forgiveness for his transgressions.

"I understand a lot of evangelicals supporting him because of his policies," Armfield said on CNN. "I'd love to see a Christian leader come out and say that they support Trump for his policies, but that his behavior disgusts them, and he needs to clean up his act."

Pastor Paula White, who serves as Trump’s spiritual advisor, says one of his most treasured possessions is a Bible signed by Rev. Graham.

“I didn’t know what to get him for his birthday and asked around and found out he wanted most was a Bible signed by Graham,” said White.

White said she gave Trump the signed Bible as a gift on his 60th birthday.

“Going to will be very impactful and meaningful on a personal level, because of their history and past,” White said of Trump attending Graham’s funeral.

Despite the family’s public role in conservative politics and its ties to Trump, the late Rev. Graham himself largely stayed away from partisan politics even as he remained close with the presidents he advised.

Graham gave the invocation for President Nixon’s inauguration in 1968, served as a spiritual adviser to President George W. Bush, and in 2010, President Barack Obama traveled to Graham’s log cabin retreat in North Carolina to meet with the Reverend and pray together.