SALT LAKE CITY — Actor Jim Caviezel says the greatest role of his life was portraying Jesus Christ in Mel Gibson's 2004 film, "The Passion of the Christ."

Caviezel's second most significant role is one he has yet to play.

In June, the 49-year-old actor will portray Timothy Ballard, the founder and CEO of Operation Underground Railroad, in a film about the organization's mission to save children from sex trafficking and slavery called "The Sound of Freedom," directed by Alejandro Monteverde.

"This is the second most important film I have ever done since 'The Passion of the Christ,'" Caviezel told the Deseret News. "It's going to affect the saving of a lot of children and the changing of lives. It will also bring a lot of light into the darkness."

With his hair dyed blonde to match Ballard's, Caviezel recently spent several days shadowing him and learning about every aspect of O.U.R.'s operation, from training on a shooting range, to seeing plans for an upcoming operation in Latin America, to meeting O.U.R.'s aftercare directors and meeting corporate partners. Their time together culminated with the premiere of a documentary called "Operation Toussaint" at Jordan Commons on May 23.

Caviezel knows he doesn't closely resemble Ballard. Caviezel has a taller, leaner frame, while Ballard is shorter with thick, muscular shoulders. But he isn't worried.

"Thankfully they can digitally make my arms bigger," Caviezel joked. "They will be bigger than his."

Introducing Caviezel to every part of the O.U.R. world has been one of the most "surreal experiences," Ballard said.

"If you can imagine taking one of your very favorite actors that you’ve watched all his films, you feel like you know this person ... and then to watch that person walk into a room having dyed his hair to look like you, to play you. That’s a surreal experience alone," Ballard said.

The experience was years in the making. Since O.U.R. started in 2013, major Hollywood studios have approached Ballard about a movie deal. The former special agent for the Department of Homeland Security and his wife would hear each pitch, then Ballard would watch for her reaction.

"Every time we would come out and she was like, nope, no way," Ballard said. "When you are making a movie and dealing with Hollywood, that's a scary thing. You don't know what to expect. The right people have to do this and it's a tricky thing to navigate. I trust my wife more than I trust me."

In 2015, a production company invited the Ballards to a screening of "Little Boy," directed by Monteverde. After the movie, at dinner, Monteverde said he wanted his next movie to be about O.U.R., Ballard said.

Ballard looked at his wife and she said "yes."

"That was it," Ballard said.

Ballard was then sequestered in a Park City cabin where the director and producer "interrogated" him for three days, recording every experience. Tears flowed as he recalled some of the details, Ballard said.

"I started opening up places in my mind that I had locked away," Ballard said. "It was therapeutic. I was crying. I didn’t expect to. I was shocked that I was so emotional. I was telling these stories that I had not ever articulated."

Eventually the story was laid out on sticky notes across a wall. When asked who he wanted to play him, Ballard's answer surprised the filmmakers.

"I said Jim Caviezel. They said he doesn’t look like you at all. I said I don’t care," Ballard said. "They said let’s try to think of somebody that looks like you. I’m like why does that matter? ... They left, and movies take forever. I thought they are never going to make this anyway."

More than two years passed. About six months ago, Ballard received a copy of the movie's script. He was informed the film's financing was secure and filming would start this summer.

Again, Ballard was asked who he wanted to portray him. He still wanted Caviezel, who impressed him with his portrayal of Edmond Dantes in the 2002 film, "The Count of Monte Cristo," as well as his other films. Ballard said his good feeling about Caviezel has been confirmed through their time together, Ballard said.

"There was something special about Jim when I watched him in the 'Count of Monte Cristo.' There was a light, to me, that came out of him," Ballard said. "It was important to us that whoever played this role had to be someone that willfully did it with God and knew that that light has to come out because we don’t want this to just be a movie, we want this to be a movement. We want this to be something that saves kids ... and warns would-be traffickers and pedophiles that we’re coming."

Before reading the script, Caviezel said he'd never heard of Operation Underground Railroad. But as a husband and father of three, he can appreciate the organization's mission and sees playing Ballard as more than just an acting job. If you are going to look into the face of evil and go after these sex traffickers, you better have a strong heart, Caviezel said.

"It's hard for people to deal with this subject but it has to be dealt with. It's a growing empire, three times bigger than the NFL. ... It's happening in every country," Caviezel said. "It has to be attacked. The screenplay is there, the director is there, the actor is there and we have a really great cast, with actors from different nations that will obviously need help on this."

In the coming weeks, Caviezel will witness a rescue operation in Latin America before filming begins in Colombia and the United States from June to September. Ballard will be on hand as a consultant for most of the filming.

In preparation, Caviezel has been right behind Ballard, observing and asking questions. While becoming Ballard is still a work in progress, Caviezel has learned a lot.

"It's more than hair color," Caviezel said. "The common bond that we have is that we were both given a great gift and we know that. I can identify (with) that. He’s really funny. So I will be able to find some humor there. He’s a tough guy. He’s cool. That will be really hard for me."

For Ballard, Caviezel's transformation is already taking place.

"He didn’t dye his hair, it’s just started changing on its own because he’s so into this," Ballard said. "He’s thinking about Tim Ballard day and night and that just started happening."

"The Sound of Freedom" is slated for release in the spring or summer of 2019.