Their story started out as if lifted from one of his love songs. Sam Cooke was 18 and Barbara Campbell was only 13 when they met on the South Side of Chicago.

Fifteen years later, Mr. Cooke, by then a pop superstar, was dead, murdered in a motel tryst gone awry. And only three months after his death, Barbara Campbell Cooke, his widow, would marry her husband’s protégé Bobby Womack, the gravelly-voiced soul singer and guitarist. Widely publicized, their union made them pariahs in their families, to much of the music community and to Mr. Cooke’s adoring fans.

In her later years Ms. Cooke lived in relative obscurity, and when she died in April at 85, no public announcement was made, at her and her family’s wish. The death was recently confirmed by David Washington, a Detroit radio host who is close to the Cooke and Womack families. No cause was given.

The Cookes’ life together and its aftermath were the stuff of Greek tragedy. Mr. Cooke, once a teenage gospel singer, was music royalty, a movie-star-handsome crooner of hits like “You Send Me” and “Wonderful World,” as well as the wrenching “A Change Is Gonna Come,” which would become a civil rights anthem.

The son of a preacher, he took a firm stand in playing the American South, refusing to perform for segregated audiences. He was a canny businessman who retained the rights to his work and built a publishing and recording company to promote the work of others. He was a voracious reader, of everything from James Baldwin to William L. Shirer’s “The Rise and Fall of the Third Reich.” (Aretha Franklin, who as a young singer was often on tour with him, remembered buying the book just because he had it.)

He was also a voracious womanizer. Mr. Cooke was 33 when he was shot by the manager of a $3-a-night motel in Los Angeles in December 1964 while chasing a prostitute who had stolen his clothes and money. Conspiracy theories still surround the death.

Barbara was his teenage sweetheart but only one of many girlfriends. She had their daughter, Linda, when she was 17; three other women would also have daughters by Mr. Cooke.

Barbara and Sam had married and divorced other people before marrying each other in Chicago in 1959, with Mr. Cooke’s disapproving father, the Rev. Charles Cook, performing the ceremony. The couple settled down in Los Angeles in a vine-covered Cape in the Hollywood area. (Mr. Cooke had added an “e” to his name at the start of his career.)

The marriage was a hard bargain. Mr. Cooke, steely in his ambition and chronically unfaithful, went about his life while Ms. Cooke fended for herself. In his exhaustive biography “Dream Boogie: The Triumph of Sam Cooke” (2005), Peter Guralnick noted how Ms. Cooke, whom he had interviewed at length, had tried to keep her end up, attempting to read James Baldwin at her husband’s prompting and joining a group of philanthropic African American women known as the Regalettes. And she had her own affairs, as she explained to Mr. Guralnick.

In 1963, their third child, Vincent, drowned in their pool when he was 18 months old. A year later, Mr. Cooke was dead.

When Mr. Cooke died, Ms. Cooke was still numb from grief over her son’s death and humiliated by the tawdry circumstances of her husband’s murder, she told Mr. Guralnick. She said she had welcomed the 19-year-old Mr. Womack into the house as a kind of protector. She was 29 at the time. At her urging, they married in early 1965.

In his own memoir, “Bobby Womack: My Story” (2006), Mr. Womack likened Ms. Cooke’s proposal to a scene out of “The Graduate,” the 1967 film in which a dazed and disillusioned young man is seduced by a friend of his parents.

“If you promise to give me five years,” Ms. Cooke told Mr. Womack, by his account, “I will give you a lifetime. You know, whatever you need to do. I just need you to walk with me here.”

Mr. Womack wrote of his new wife: “She could, and did, take a lot. She could endure.” He added: “She and Sam were a pair. They lived each other. They really did.”

But it upset many people to see Mr. Womack, sometimes in Mr. Cooke’s clothes, squiring Mr. Cooke’s widow about. The couple received hate mail, including a package containing a baby doll in a coffin. At a Nancy Wilson concert, when Ms. Wilson introduced the couple sitting in the audience, the crowd booed. In his telling, Mr. Womack, goaded by his new wife, took to cocaine. He also began a sexual relationship with the Cookes’ daughter, Linda, by then a teenager. When Barbara found them in bed, she shot Mr. Womack, the bullet grazing his temple. (Ms. Cooke was not charged, according to Mr. Womack’s book.) They divorced in 1970.

Years later, Linda Cooke married Mr. Womack’s brother Cecil, and the couple became a recording duo, Womack & Womack. Linda now goes by the name Zeriiya Zekkariyas, a nod to her African heritage.

Ms. Cooke and Bobby Womack had a son, whom they named Vincent, after the Cookes’ drowned baby. Vincent Womack struggled with drugs and alcohol, his father wrote, and committed suicide in 1986 when he was 21.

Bobby Womack experienced fame early on when the Rolling Stones covered his 1964 song “It’s All Over Now,” their first No. 1 hit. He died in 2014 at 70, but not before suffering other tragedies. Another son of his, Truth, died when he was a baby, and Mr. Womack’s brother Harry was murdered by a girlfriend.

“I don’t speak to Barbara no more,” Mr. Womack wrote in his memoir. “Linda doesn’t speak to her. Haven’t spoken to Cecil for years. No one speaks to no one.”

Barbara Campbell and her twin sister, Beverly, were born on Aug. 10, 1935, in Chicago. She attended Doolittle Elementary School. Mr. Cooke had graduated from high school when they met, but Barbara, a teenage mother, worked two jobs to support herself and her child.

In 1986, when Mr. Cooke was inducted into the Rock & Roll Hall of Fame, Ms. Cooke stood by Mr. Cooke’s father to accept the award on the singer’s behalf.

“I think if Sam were able to be here tonight, he would be thrilled just to see me on this stage,” Mr. Cooke’s father declared. (The elder Mr. Cook had not initially been thrilled with his son’s transition from gospel to secular music.)

Ms. Cooke is survived by Ms. Zekkariyas and another daughter, Tracey Cooke; her twin sister, Beverley Lopez; and a granddaughter.

Family members and Mr. Guralnick declined to speak about Ms. Cooke’s life and death, citing her wish for privacy.

But Ms. Cooke had the last words in Mr. Guralnick’s nearly 750-page biography. The author quoted her reminiscing about falling in love with Mr. Cooke, and he with her, and about their wandering through Chicago’s Ellis Park in the snow when they were teenagers.

“We’d walk around the park and fantasize,” she told Mr. Guralnick. “We didn’t have a dime between us, but you’d have thought I was the princess and he was the prince. Every time a Cadillac went by, I’d say, ‘That’s our chauffeur. He’s coming to take us to our mansion.’”

She added: “Everybody wants a happy ending. That’s the way I see it.”