Ralph Abernathy and the Rev. Will D. Campbell at the Lorraine Motel in Memphis after the assassination there of Martin Luther King Jr. in 1968. (Henry Groskinsky/LIFE)

The Rev. Will D. Campbell, a self-described “bootleg preacher” who became one of the most prominent white clergymen in the South to fight for racial equality during the civil rights movement, died June 3 at a nursing home in Nashville. He was 88.

He had complications from a stroke two years ago, said his friend John Egerton.

Rev. Campbell was ordained a minister while still in his teens but came to distrust organized religion and to prefer preaching anywhere, as he liked to say, but under a steeple. He documented his life and philosophy in more than a dozen books, including “Brother to a Dragonfly,” a finalist for a 1978 National Book Award.

Growing up during the Great Depression, he lived on a small Mississippi cotton farm. He understood the struggles and fears of poor whites in the South and sought not to judge the racists among them. “Mr. Jesus died for the bigots as well,” Rev. Campbell was quoted as saying.

At the same time, he observed the indignity suffered by blacks in the Jim Crow era and dedicated nearly his entire adult life to bringing it to an end. Trusted by both blacks and whites, he straddled the two worlds of the segregated South and was present at some of the seminal moments of the civil rights movement.

“Will Campbell was one of the few people who could offer support on both sides,” Bernard LaFayette Jr., a Baptist minister and civil rights leader, said in an interview. “Blacks needed to know that there were whites who supported what they were doing . . . and then there were those whites who were absolutely convinced that things could never change.”

Rev. Campbell was reportedly the only white person present at the founding in 1957 of the Southern Christian Leadership Conference, the civil rights organization then led by Martin Luther King Jr. and other major figures in the movement. Initially, some of the black organizers argued against admitting him.

“Let this man in,” said Bayard Rustin, one of the leaders, according to an account published in the Nashville Tennessean. “We need him.”

When King was assassinated in 1968 at the Lorraine Motel in Memphis, Rev. Campbell rushed to the scene. Photos captured by a photographer for Life magazine show him standing, weary and seemingly dumbstruck, on the hotel balcony and grieving with the black leaders left to carry on.

Later, Rev. Campbell drew criticism from some in the civil rights movement when he visited James Earl Ray, King’s assassin, in prison, and when he ministered to a Ku Klux Klan grand dragon in jail.

Rev. Campbell supported the integration of schools across the South, most notably in 1957, when he accompanied black students as they braved a mob in an effort to enter Central High School in Little Rock. In 1963, when four young black girls were killed in the bombing of the 16th Street Baptist Church in Birmingham, Ala., Rev. Campbell came to comfort their families.

“He was a walking nerve center,” the late journalist David Halberstam once told Rolling Stone magazine. “He was enormously important but so deft and nimble that the reactionaries never caught on to him. His fingers were everywhere, but when you looked around — there were no fingerprints. He was the Invisible Man.”

Will Davis Campbell was born July 18, 1924, in Amite County, Miss., and was baptized in a river. The Bibles at his church were emblazoned with the sign of the KKK, the Tennessean reported. He credited his family with raising him to be racially tolerant.

During World War II, Rev. Campbell served as an Army medic in the Pacific. After the war, he received a bachelor’s degree in English from what is now Wake Forest University in Winston-Salem, N.C., and a divinity degree from Yale University in 1952.

Rev. Campbell’s moniker for himself — bootleg preacher — perhaps referred to several aspects of his identity. For one, he had a taste for moonshine. For another, he emerged early on as a rebel within the church.

He served briefly as the pastor of a small Baptist church in Louisiana, but he did not care for the job, and some parishioners reportedly did not care for him, his sermons on civil rights or his tendency to crop up on picket lines. “I was trained to be a minister, but I didn’t make it,” Rev. Campbell once told National Public Radio. “Either they weren’t ready for me or I wasn’t ready for them.”

After leaving the traditional ministry, he became director of religious life at the University of Mississippi in 1954, the year that the U.S. Supreme Court declared segregated public schools unconstitutional. Rev. Campbell caused a ruckus when he played ping-pong with a black minister. He wryly reassured a dean that they had used “separate but equal paddles,” the Tennessean reported.

Rev. Campbell later worked with the National Council of Churches and the Committee of Southern Churchmen. His books ranged from reflections on his upbringing to meditations on Christianity to novels. “Brother to a Dragonfly,” his best-known volume, was about his relationship with his brother, Joe, and how Rev. Campbell adopted his particular faith.

The memoir, book critic Jonathan Yardley wrote in The Washington Post in 1977, “is really two books in one, and what is so remarkable is that both of them are so good.”

Rev. Campbell’s honors included a National Humanities Medal from President Bill Clinton. Survivors include his wife of 67 years, Brenda Fisher Campbell of Nashville; three children, Penny Campbell and Webb Campbell, both of Nashville, and Bonnie Campbell of Durham, N.C.; a brother; and four grandchildren.

Rev. Campbell had a simple explanation for the ministry to which he devoted his life.

“If you’re gonna love one,” the Tennessean quoted him as saying, “you’ve got to love ’em all.”