The Rev. Ralph David Abernathy, who created the civil rights movement with Martin Luther King Jr. but decades later enraged the slain leader’s supporters by writing about his alleged infidelity, died Tuesday.

Abernathy, who had cradled the fallen King’s bloodied head after he was struck down by a bullet in 1968, was 64.

Abernathy died at 12:10 p.m. at Crawford Long Hospital, said hospital spokesman Mendal Bouknight. He had been undergoing a lung scan when his heart stopped, and efforts to revive him in an operating room failed, Bouknight said. Abernathy had been in the hospital since last month for treatment of a sodium deficiency. He had suffered strokes in 1983 and 1986. Abernathy spent his last months under bitter criticism from his colleagues for passages in his 1989 autobiography, “And The Walls Came Tumbling Down.” He wrote that King had spent time with two women and had a violent argument with one in the 24 hours before his 1968 assassination.

But the Rev. Joseph Lowery, who succeeded Abernathy as president of the Southern Christian Leadership Council, described Abernathy on Tuesday as “a faithful servant of the cause of liberty and justice.” “I extend my love and support to his family,” he said. King’s son, Fulton County Commissioner Martin Luther King III, called Abernathy’s death “a very tragic loss to our nation.”

Abernathy was pastor of Atlanta’s West Hunter Street Baptist Church and president emeritus of the SCLC, which he founded with King in 1957 as a vehicle for the movement they began with the 1955 bus boycott in Montgomery, Ala. Abernathy had said he had no desire to lead the movement, preferring to leave that role to the more charismatic King. But two days after King’s assassination, the remaining aides picked him as SCLC president, according to King’s wishes. He left the SCLC presidency in 1977, when he resigned to run for Congress. He was defeated in the Democratic primary. In 1980, he supported Ronald Reagan in his presidential bid. Abernathy suffered a stroke in 1983 and underwent brain bypass surgery at Johns Hopkins Hospital in Baltimore. After he recovered, he returned to preach at West Hunter, where he had been pastor since 1961, and backed Jesse Jackson in his 1984 presidential bid.

When Abernathy mentioned King’s relationships with women in his book, he became the first of King’s inner circle to do so, even though the matter had been chronicled by several noted biographers.

Black leaders asked Abernathy to retract the passages, and insinuated that his memory had been impaired by the strokes and brain surgery. But Abernathy, whom King praised as his closest friend and confidant, insisted the accounts were true. Abernathy, born March 11, 1926, in Linden, Ala., was King’s right-hand man for 13 years, sharing jail cells with him, traveling with him and advising him. “We were known as the civil rights twins,” Abernathy once recalled. “We always sought to complement each other. I never tried to be a copy of him and he never tried to be a copy of me.” It was Abernathy who comforted King’s head as he lay dying of a bullet wound on the balcony of the Lorraine Motel in Memphis, Tenn., on April 4, 1968. He took care of various funeral details for King’s widow, Coretta Scott King, and delivered the eulogy. Although he helped found the civil rights movement, stood at King’s side through the great battles and went to jail as often as King did, Abernathy consistently found himself in King’s shadow. And it bothered him. In a 1986 interview, he lamented that once, when he visited a school in Connecticut, “not a single student knew who I was.”