Madame Ngo Dinh Nhu, the first lady of South Vietnam during the 1950s and early 1960s whose venom-glazed tongue and scalding temper made her an influential and deeply feared political figure, died April 24 at a hospital in Rome.

She was 87, according to a BBC report, which gave no cause of death. Mme. Nhu had lived as a widow in European exile since 1963, when her husband and brother-in-law were killed in a coup.

Mostly living in obscurity ever since, she had once been among the world’s most visible women. She was featured on the cover of Time and Life magazines and became the glamorous public face of the South Vietnamese regime in media interviews and international speaking tours.

Born Tran Le Xuan, which means “beautiful spring,” she had grown up amid privilege and had family connections to Vietnamese aristocracy. She asserted political power through her marriage to Ngo Dinh Nhu, the chief of the secret police and adviser to the autocratic regime controlled by his brother, Ngo Dinh Diem.

Because Diem was a lifelong bachelor, Mme. Nhu took the title of first lady, said William Prochnau, a former Washington Post foreign correspondent in Vietnam who wrote the 1995 book “Once Upon a Distant War: Young War Correspondents and the Early Vietnam Battles.”

“It was almost as if she was married to Diem instead of his brother Nhu,” Prochnau said in an interview. “He listened to her more than anybody in Vietnam.”

In his book, Prochnau wrote that Mme. Nhu was a “starkly beautiful woman,” equipped with “scalpel-like scarlet fingernails,” who resembled the cartoon femme fatale “Dragon Lady” in the popular comic strip “Terry and the Pirates.”

“Everybody called her that, even in the U.S. Embassy in confidential reports,” Prochnau said in the interview. “It wasn’t just the press. She fit the part — in looks, activities and actions.”

Diminutive and wasp-waisted, she was often photographed in captivating poses and attire, including a form-fitting, low-cut variation of the traditional Vietnamese silk tunic known as the ao dai.

Mme. Nhu — through her sex appeal, fist-pounding persistence and sporadic charm offensives — came to possess tremendous influence on the affairs of state. Army generals took orders from her. The president did too.

When Mme. Nhu stepped into the room, photographers took notice and reporters scrambled for notebooks. In her public remarks, she could be scathing and callous. She once quipped that she would bring mustard to the “barbeque” when a Buddhist monk set himself on fire to protest Diem’s tyranny.

Mme. Nhu’s ferocious personality became legend shortly after Diem became president of the newly independent South Vietnam in 1954.

At the time, the army was still controlled by generals who were loyal to the former French colonial rulers and who regularly threatened to take power in a coup.

Time magazine reported in 1963 that one Army general, Nguyen Van Hinh, joked at cocktail parties that if he led a coup, he would exile every member of Diem’s family except Mme. Nhu. He said she would be his concubine.

“You are never going to overthrow this government because you don’t have the guts,” Mme. Nhu later told the general. “And if you do overthrow it, you will never have me because I will claw your throat out first.”

Not long after, Mme. Nhu was elected to the National Assembly and portrayed herself as a symbol of feminist might.

As one of a handful of women in the 123-member National Assembly, Mme. Nhu helped pass legislation that aimed to empower women, including a bill that ended polygamy.

Mme. Nhu, a devout Catholic who wore a diamond-studded crucifix around her neck, also helped pass bills that banned abortion, boxing, beauty contests, contraception, cockfights and dancing.

She founded a women’s solidarity movement that grew to 1.2 million members and organized an elite women’s paramilitary corps. She referred to the soldiers as “my darlings.”

Mme. Nhu saw herself as a patriot and revolutionary surrounded by enemies. In February 1962, two dissident military pilots bombed and strafed the palace in Saigon while Mme. Nhu, her children, husband and Diem were inside. Mme. Nhu fell through a hole in the rubble from her bedroom to the basement two stories below.

She later told reporters: “I never have been afraid of death. I am still unafraid.”

Mme. Nhu openly blamed much of her country’s turmoil on Vietnam’s Buddhist majority. After monks began to protest the Diem government by self-immolation, Mme. Nhu ridiculed the fiery suicides as publicity stunts.

“I would clap hands at seeing another monk barbeque show,” Mme. Nhu wrote in a letter to the New York Times in August 1963, “for one cannot be responsible for the madness of others.”

Mme. Nhu’s father, Tran Van Chuong, resigned that month as South Vietnam’s ambassador to the United States as a protest against the suppression of Buddhists.

After weeks of violent demonstrations, the Diem regime was toppled on Nov. 1, 1963, in a bloody coup that was later revealed to be supported by the U.S. government. Diem and Mme. Nhu’s husband were killed and buried in unmarked graves.

Mme. Nhu — who was in Beverly Hills at the time — immediately fled to Europe, where she spent the rest of her life, dividing her time between Paris and Rome.

In a rambling statement she released after the coup, Mme. Nhu wrote, “If really my family has been treacherously killed with either the official or unofficial blessing of the American Government, I can predict to you all that the story in Vietnam is only at its beginning.”

Mme. Nhu was born in 1924 in Hanoi, where her father was a wealthy landowner and her mother a descendent of Vietnamese royalty.

Mme. Nhu grew up with 20 personal servants and was educated in a prestigious French-language school. At 18, she married Ngo Dinh Nhu, a politically connected family acquaintance who was 15 years her senior. She converted from Buddhism to Catholicism, which was his family’s faith.

In 1946, Mme. Nhu and her infant daughter were taken prisoner by communist forces. They spent four months in a jungle village surviving on two bowls of rice a day. She eventually escaped and settled with her husband in Dalat, a mountainous town in South Vietnam.

From there, Mme. Nhu and her husband helped organize popular support to bring Diem to power.

Her years in exile were marked by continued tragedy. In 1967, her daughter Le Thuy was killed in a traffic accident in Paris. Mme. Nhu’s parents stayed in Washington after the 1963 coup and were killed in 1986 by their son Khiem, who authorities said was motivated by a dispute about his inheritance. A judge ruled him mentally unfit for trial and he was released in 1993 after spending seven years at St. Elizabeths Hospital.

Mme. Nhu is survived by three children.