Dr. Martin Luther King Jr's "I Have a Dream Speech" is one of the most famous addresses in world history, but the remarks have remained off screen in the few biopics created about the late civil rights activist. Attorney Clarence Jones filed the copyright for the speech for King in 1963. Since his death, the executors of King's estate—his children Bernice, Dexter, and Martin III—have refused most filmmakers' requests to use the speech and King's other quotes and writing.

"The short answer is that those words are legally off-limits without getting permission," says Kent Germany, an associate professor of history at the University of Southern Carolina. "Securing those rights poses a major hurdle—and likely a major expense—for any filmmaker."

King has received only one major biopic, 2014's Selma, directed by Ava DuVernay. (For context, the world has endured at least three Elizabeth Taylor biopics.) Instead of using King's speeches, DuVernay wrote original monologues that sounded like soliloquies the civil rights leader could have given. For instance, as the Hollywood Reporter pointed out, King says, "Who murdered Jimmie Lee Jackson?" in the movie instead of the historical quote, "Who killed him?" When asked about the changes in 2014, DuVernay told the Washington Post, "We knew those rights are already gone. They're with Spielberg."

In 2009, Steven Spielberg's DreamWorks company paid the estate for film rights to King's words, along with his life rights, which allow a person or company to make content based on an individual's story. DreamWorks has yet to produce or direct Spielberg's planned King biopic, but the rights have caused complications for numerous filmmakers. (Neither Spielberg's literary agent nor King's estate returned Broadly's request for comment.)

In 2011, Universal cancelled director Paul Greengrass's biopic, Memphis. According to Deadline, there were rumors that the estate strong-armed the company into dropping the movie. In the same year, Warner Bros. cancelled their own project, instead joining DreamWorks to co-produce a film with the support of the King estate.

Spielberg has yet to direct a movie about King. At an American Film Institute event, he approached David Oyelowo, who played King in Selma, about potentially starring in his King biopic. "[He] came up to me and said, 'My goodness, David, [Selma is] one of the best things I have ever seen. You really inspired me to take another look at my Dr. King film,'" Oyelowo told Esquire. "And then he goes, 'You would reprise the role, right? You would do it again?' My stomach all but fell out of my body. I was just like, 'Oh, my lord.' That was quite a mountain to climb. Not only did idea of being asked to do it again give me pause, but here he is, Steven Spielberg of all people, [asking] if I entertain doing it again."

The Hollywood drama over his quotes in films coincide with other problems in King world. Three years ago, Martin III and Dexter sued their sister, Bernice, because she rejected their bid to auction King's Nobel Peace Prize medal and travel Bible, which Barack Obama used when he was sworn into office.

The case was settled last year (it's unclear if they will sell the items), but other controversies have erupted. Last fall, the National Museum of African American History and Culture opened without any of King's belongings, because the estate would not loan them to the Smithsonian Institute.

"It's outrageous," Jones, the late King's attorney told the Washington Post at the time. "This is the Smithsonian. This is not just another party. This is one of the most important institutions now in the 21st century. And this is probably the greatest civil rights leader in the 20th century. I find it shameful and I'm sad."

Four years earlier in 2011, the siblings also charged a non-profit $800,000 to use King's words at his monument on the Mall in Washington DC, according to the same Post story.

After King was assassinated, though, his children had little financial support. Using his accomplishments for business was one of their few options. Their reservations for their father's words in films fall in line with numerous business decisions over the years.