Mother Antonia holds hands with inmates in 2002 in the chapel at La Mesa prison in Tijuana, where she lived for more than 30 years. (Mary Jordan/The Washington Post)

Mary Clarke grew up in the luxury of Beverly Hills, where movie stars, such as William Powell, Hedy Lamarr and Dinah Shore, were among her neighbors. She spent weekends at a roomy beach house overlooking the Pacific and once had closets filled with mink coats and ball gowns.

She was married two times, raised seven children and managed her father’s office-supply business after his death. In the midst of this busy life, she devoted more and more time to charity, which she considered a crucial part of her Catholic faith.

In 1965, she accompanied a priest on a mission to deliver medicine and other supplies to Tijuana, Mexico. After several other stops, they ended up at the gate of one of the country’s most notorious prisons, a state penitentiary called La Mesa. The warden invited them inside to drop off their donations at the infirmary.

She began to visit the prison more often, attending to the needs of the inmates, guards and police, and the transformation of Mary Clarke Brenner had begun. In 1977, when most of her children were grown, she moved to La Mesa.

Although she had no formal religious training, she sewed her own nun’s habit and slept in a bunk in the women’s wing of the prison. She later lived for years in a 10-by-10-foot cell, with the walls painted pink.

She made it her vocation to attend to the needs of some of the most destitute and dangerous people in Mexico. She brought them medicine, bedding, clothing and food. She invited doctors and dentists from California to provide medical care. She worked with Mexican officials to improve conditions in La Mesa and other prisons.

When she walked through the halls, prisoners kissed her hand, and she kissed theirs. Notorious criminals confessed to her and pledged to change their lives.

In Tijuana and throughout all of Mexico, she was known as “Madre Antonia” — Mother Antonia.

She received the blessings of a Mexican bishop of the Catholic Church, was greeted by Pope John Paul II and was commended by Mexican President Vicente Fox. She went on to found a religious order for older women seeking to help the poor.

Mother Antonia went on to live in the prison for more than 30 years, improving the lives of thousands of prisoners, guards and their families. Mother Antonia was the subject of a 2005 book by Washington Post journalists Mary Jordan and Kevin Sullivan, “The Prison Angel,” and a later documentary film.

After years of weakening health, she died Oct. 17 at the Tijuana headquarters of the religious order she founded, Sisters of the Eleventh Hour of St. John Eudes. She was 86.

She had heart ailments and myasthenia gravis, a neuromuscular disorder. A daughter, Carol Brenner, confirmed the death.

“Something happened to me when I saw men behind bars,” Mother Antonia told the Los Angeles Times in 1982. “When it was cold, I wondered if the men were warm; when it was raining, if they had shelter . . . You know, when I returned to the prison to live, I felt as if I’d come home.”

She was born Mary Clarke in Los Angeles on Dec. 1, 1926. Her father became the owner of a prosperous office-supply business and moved the family to Beverly Hills.

At 19, Mary Clarke married Ray Monahan. After their first child died in infancy, they had two more children before they divorced.

In 1950, she married Carl Brenner, with whom she had five more children before their eventual divorce. Mother Antonia was fully aware of the irony of a divorced woman donning a religious habit, but she remained close to her children after moving to Tijuana.

“She was extremely attentive and caring, even though far away,” her daughter Carol said in an e-mail. “We spoke by telephone nearly every day.”

At times, her daughter noted, “I could hear the bullets shot outside, hitting the walls of her cell. . . . She wasn’t fearful at all, but I was.”

Survivors include her seven children, 11 grandchildren, 28 great-grandchildren and two great-great-grandchildren.

Mother Antonia wore a cross made by inmates from nails and copper wire. It had a large Star of David at its center, symbolic of her father’s respect for Jewish people and her own sense of open-armed acceptance.

La Mesa prison held as many as 7,500 inmates at a time, and in some ways it was like a village, with shops, food and services being sold and traded. Mother Antonia said she even had kittens nesting outside her door.

One of her most trying moments came on Halloween night in 1994. Some prisoners took guards hostage and captured their guns, and a full-scale riot broke out. Parts of the prison were on fire.

Amid smoke, screams and gunshots, the 5-foot-2 Mother Antonia walked through the halls, wearing her customary black-and-white habit. The warden told her to seek safety. Even the prisoners warned her that her life was in danger.

She kept walking. First, a few men followed. Then she drew a larger crowd of prisoners behind her. She quietly addressed the prisoners as she always did, calling out, “My sons.”

“I said, ‘The guns,’ ” she told Terry Gross of NPR’s “Fresh Air” in 2005. “ ‘Give me the weapons right now, sons. Give them to me. God is watching. God is with us, and we’re going to help you.’ ”

The prisoners laid down their weapons, and the riot came to end.

Mother Antonia negotiated a truce and told the inmates they would not be punished. She took their grievances to the warden, and conditions quickly improved.

“I am hard on crime, but not on persons,” she told The Post in 2002. “Everyone deserves to be treated with dignity.”

The prison warden, Carlos Lugo Felix, had another name for Mother Antonia: “There is no other way to describe her. She is a saint.”