He was MLK's mentor, and his meeting with Gandhi changed history. But Howard Thurman was largely unknown, until now

The Rev. Howard Thurman was a spiritual genius who shaped much of 20th century America but his introverted persona kept him away from the spotlight.

(CNN)A visitor seeking advice from the Rev. Howard Thurman one day was talking about what the world needs when Thurman interrupted him.

"Don't ask what the world needs, ask what makes you come alive, and go do it," Thurman told him. "Because what the world needs are people who have come alive."
Thurman's response went viral before the term was invented. It's been cited by everyone from cultural icon Oprah Winfrey to countless inspirational speakers. It's even become an internet meme. But what makes those words stick is that Thurman validated them by the way he lived.
He was a shy man who didn't lead marches or give dramatic speeches. But he was full of big ideas that changed the world. He pioneered a form of spiritual activism that blended contemplation with confrontation. He was "one of the unacknowledged shapers of 20th century America," according to one historian.
    They called the Rev. Howard Thurman a mystic but his friends and students said he was a mesmerizing storyteller and a genuinely kind man.
    Thurman forged a connection between Mohandas Gandhi and the Rev. Martin Luther King Jr. that gave wings to the civil rights movement. He wrote a bombshell of a book that revolutionized the traditional portrait of Jesus. And he still inspires leaders as diverse as civil rights icon John Lewis, the Democratic congressman from Atlanta, and Barbara Brown Taylor, a celebrated author and speaker.
    "Howard Thurman was a spiritual genius who transformed persons who transformed history," is how Luther E. Smith, Jr., author of "Howard Thurman: The Mystic as Prophet," once described him.
    Now a broader audience is being offered their own chance to meet Thurman. Starting Friday, PBS stations will air "Backs Against the Wall: The Howard Thurman Story." The 55-minute film explores how Thurman went from a lonely African-American boy who talked to an oak tree for companionship to a man who still speaks to spiritual seekers nearly 40 years after his death.
    Martin Doblmeier, the film's director, said Thurman's voice is needed even more today because of pervasive political and religious tribalism. Thurman constantly sought common ground with people who were different.
    He calls Thurman the "patron saint of those who say I'm spiritual not religious."
    "He can put angry hearts at ease," he says. "You can't read Howard Thurman and come away with an angry heart."

    Thurman's deep connection with MLK

    He also took risks.
    He was the first pastor to co-found an intentionally multiracial and multifaith church in the United States.
    He was the first African-American pastor to travel to India and meet Gandhi. (Gandhi ended their meeting by asking Thurman to sing a Negro spiritual).
    And he was one of the first pastors to inspire King to merge Gandhi's philosophy of nonviolent resistance with the civil rights movement.
    Thurman's connection with King went way back. He was a classmate of King's father, "Daddy King," at Morehouse College. And he became dean at Boston University's Marsh Chapel while King was enrolled at the university. While King was studying for his doctorate at the university, he would attend chapel service and take notes while Thurman preached.
    King would often stop by Thurman's house on Sunday afternoons for another ritual: watching Jackie Robinson play baseball on TV.
    "There's this fatherly sense, this spiritual mentorship that Thurman provides to Martin Luther King, Jr.," Doblmeier says.
    The Rev. Martin Luther King Jr. shared a belief in "prophetic spirituality" and a fondness for Jackie Robinson with Howard Thurman.
    King quickly got a chance to apply the lessons he learned from hearing Thurman preach. Six months after earning his doctorate, he led his first nonviolent mass protest in Montgomery, Alabama. Thurman's concepts about nonviolence and Jesus are peppered through some of King's writings.
    "One cannot understand King's philosophy and theology without first understanding Thurman's work and Thurman's influence on King and other civil rights leaders," says David B. Gowler, co-editor of "Howard Thurman: Sermons on the Parables."
    Gowler called Thurman one of the overlooked heroes of the civil rights movement. Yet he wasn't a traditional preacher-activist. One pastor in the film quipped that many expected Thurman to be a Moses, but instead they got a mystic.

    The essence of Thurman's message

    Thurman embodied what some call a "prophetic spirituality." He talked constantly about the "inward journey." But he wasn't interested in any theology preoccupied with the self. He thought personal transformation should be accompanied by a "burning concern for social justice."
    Gowler calls Thurman a "spiritual activist." So was Thurman's wife, Sue Bailey Thurman,
     When Howard Thurman met Mohandas Gandhi, they had a lengthy conversation that ended with Gandhi asking him to sing a Negro spiritual.
    "He was fundamentally both a teacher and pastor to others in the civil rights movement," says Gowler, a religion professor at Oxford College of Emory University in Georgia.
    Thurman was also another type of pioneer, the film shows. Long before the term "interfaith dialogue" became common, Thurman worshiped with people of other faiths and warned about the dangers of religious fundamentalism.
    He once told the BBC that "theologies are inventions of the mind" designed to "imprison religious experience." But the religious experience itself will always be one step ahead of dogma because it is "dynamic and fluid."
    "Whether I'm black, white, Presbyterian, Baptist, Buddhist, Hindu, Muslim -- in the presence of God all of these categories by which we relate to each other fade away," Thurman says during another interview in the film.
    The film also explores Thurman's best-known work, "Jesus and the Disinherited," which was published in 1949. The book was a condemnation of an "otherworldly" Christianity, which Thurman said was far too often "on the side of the strong and the powerful against the weak and oppressed."
    A person can't grasp Jesus' message without first understanding the anger and fear that he grappled with as a member of a despised minority under Roman occupation, Thurman argued in the book.
    "Jesus was a Jew. Jesus was a poor Jew. Jesus was a poor Jew from a minority group. Thurman makes the point that if Jesus were kicked into the ditch by a Roman soldier, he would be just another Jew in a ditch," Gregory Ellison II, an activist who is working on a book on Thurman, says in the film.

    The 'sound of the genuine'

    Thurman knew what it felt like to be despised. He was born in 1899 in Daytona Beach, Florida, during the "nadir" of race relations in post-Civil War America. Lynching was common, discrimination legal and the Ku Klux Klan was so popular it held a massive march on Washington when he was a young man.
    He was 7 when his father died. He was raised in part by his grandmother, Nancy, who had been enslaved. She was illiterate, but he saw her as his first spiritual genius.
    "I learned more, for instance, about the genius of the religion of Jesus from my grandmother than from all the men who taught me all ... the Greek and all the rest of it," he once said.