Gregory Allen Howard, the screenwriter behind Harriet, spent two decades pushing for his film before the action-adventure biopic about the African American abolitionist and icon finally arrived earlier this month.

In an interview with Focus Features about the film, Howard revealed the challenges he was up against, including an executive who didn’t think it was necessary for Harriet Tubman to be played by an African American woman.

“The climate in Hollywood, however, was very different back then,” he said. “I was told how one studio head said in a meeting, ‘This script is fantastic. Let’s get Julia Roberts to play Harriet Tubman.’ When someone pointed out that Roberts couldn’t be Harriet, the executive responded, ‘It was so long ago. No one is going to know the difference.’”

Thankfully, Tubman was portrayed by Cynthia Chinasaokwu O. Erivo, the Tony and Grammy awarded actress who performed as Celie in the Broadway adaptation of The Color Purple.

“I first saw her when the other producers flew me to New York to see her in The Color Purple,” Howard said of Erivo. “As soon as she opened her mouth, I thought, ‘Yes, that’s Harriet.’ Afterwards I emailed the other producers, ‘That’s Harriet. She’s a little stick of dynamite.’”

The Harriet cast also includes, Leslie Odom Jr., Janelle Monae, Jennifer Nettles and Joe Alwyn. Howard says “nearly all” of the film’s characters are based on real people.

In the interview, Howard also credited two films for helping Harriet become a reality, 12 Years a Slave and Black Panther.

“When 12 Years a Slave became a hit and did a couple hundred million dollars worldwide, I told my agent, ‘You can’t say this kind of story won’t make money now,’” he explained. “Then Black Panther really blew the doors open.”

Harriet, directed by Kasi Lemmons, hit theaters on Nov. 1.

“For me, this film is my valentine to black women. I wanted them to be able to go to the movies on Saturday and see this young black woman take on this incredible power structure and triumph over it,” Howard, who has also penned Remember the Titans and Ali, said.

“Harriet was bigger than life,” he concluded. “Harriet freeing slaves had a multiplying effect.”