Izola Ware Curry, the mentally ill woman who in 1958 stabbed the Rev. Dr. Martin Luther King Jr. at a Harlem book signing — an episode that a decade later would become a rhetorical touchstone in the last oration of his life — died on March 7 in Queens. She was 98.

Ms. Curry died in a nursing home, the last stop in the series of institutions that had been her home for more than half a century. Her death, confirmed by the office of the chief medical examiner of New York City, was first reported by The Smoking Gun, the investigative website.

What surprised many observers at the time of the crime was that Ms. Curry herself was black, the daughter of sharecroppers from the rural South. Questions persisted about what could have moved her to attack Dr. King, then a 29-year-old Alabama preacher who had assumed the national stage amid the Montgomery bus boycott of 1955-56.

The stabbing nearly cost Dr. King his life, requiring hours of delicate surgery to remove Ms. Curry’s blade, a seven-inch ivory-handled steel letter opener, which had lodged near his heart. If he had so much as sneezed, his doctors later told him, he would not have survived.

The letter opener Izola Ware Curry used to stab the Rev. Dr. Martin Luther King Jr. protruded from his chest after the attack. CreditVernoll Coleman/New York Daily News

Dr. King, who said afterward that he bore no animus toward Ms. Curry and did not want charges pressed, memorialized the attack in “I’ve Been to the Mountaintop.” That speech, delivered in Memphis on April 3, 1968, the day before he was assassinated, endures as one of his most famous.

“The X-rays revealed that the tip of the blade was on the edge of my aorta, the main artery,” Dr. King said in the speech. “And once that’s punctured, you’re drowned in your own blood — that’s the end of you.”

Of all the letters of consolation that poured in to the hospital, he continued, there was one that “I will never forget.”

“Dear Dr. King,” it read. “I am a ninth-grade student at the White Plains High School. While it should not matter, I would like to mention that I’m a white girl. I read in the paper of your misfortune, and of your suffering. And I read that if you had sneezed, you would have died. And I’m simply writing you to say that I’m so happy that you didn’t sneeze.”

To impassioned applause, Dr. King went on: “And I want to say tonight — I want to say tonight that I, too, am happy that I didn’t sneeze. Because if I had sneezed, I wouldn’t have been around here in 1960, when students all over the South started sitting in at lunch counters.”

If he had sneezed, he continued, he would not have seen the Freedom Rides of the early ’60s, nor given his “I Have a Dream” speech at the Lincoln Memorial in 1963, nor seen the passage of the federal Civil Rights Act of 1964, nor been involved in the Selma-to-Montgomery marches of 1965.

And so, Dr. King concluded, “I’m so happy that I didn’t sneeze.”

He was shot to death by James Earl Ray in Memphis the next day.

Apart from Dr. King’s speech, Ms. Curry vanished from history. Deemed unfit to stand trial, she was committed to a mental hospital; as the years elapsed and no more was heard of her, she was widely presumed dead. Even a 2002 book about the stabbing, “When Harlem Nearly Killed King,” by Hugh Pearson, does not chart her life’s later course.

Then, in a profile published last August, The Smoking Gun wrote of having found Ms. Curry, physically and mentally feeble, at the nursing home, Hillside Manor, in the Jamaica section of Queens.

“While Curry described her daily routine — up at 5:30 a.m., bed around 10 p.m., and not much going on in between,” the profile said, “she met questions about King and the stabbing with a furrowed brow and a blank stare.”

Izola Ware was born on June 14, 1916, near Adrian, a village in east-central Georgia. She appears to have had little education beyond grade school.

After a brief early marriage to James Ware dissolved, Ms. Curry moved to New York, where she found work as a domestic. There, she began to experience the paranoid delusions that would overtake her completely before she was 40.

Her mental state made it increasingly hard for her to hold a job. As Mr. Pearson’s book reported, she bounced among New York; Cleveland; St. Louis; Charleston, W.Va.; Savannah, Ga.; Miami, West Palm Beach and Daytona Beach, Fla.; Lexington, Ky.; and Columbia, S.C. By 1958 she was back in New York, living in a rented room in Harlem, at 121 West 122nd Street.

“To her neighbors she was a very antisocial woman,” Mr. Pearson wrote. “Curry spoke with a distinct Southern accent, but her words were often unintelligible.”

A half-dozen years earlier, she had begun having delusions about theNational Association for the Advancement of Colored People, which she believed was a Communist front. In her mind, the group was persecuting her — following her and making it impossible for her to find steady work. She wrote letters to that effect to the Federal Bureau of Investigation.

Over time, as Dr. King rose to prominence, her delusions centered increasingly on him.

On the afternoon of Sept. 20, 1958, Dr. King was autographing copies of his first book, “Stride Toward Freedom: The Montgomery Story,” in Blumstein’s department store, at 230 West 125th Street.

Ms. Curry, elegantly attired in a stylish suit, jewelry and sequined cat’s-eye glasses, entered the store armed with a loaded .25-caliber automatic pistol and the letter opener. The pistol was secreted in her bra, the letter opener in her handbag. She pushed her way through the crowd to the table where Dr. King sat.

“Are you Martin Luther King?” she asked.

“Yes,” he replied, not looking up from the book he was signing.

She reached into her handbag.

“The next minute,” Dr. King later wrote, “I felt something beating on my chest.” He was taken to Harlem Hospital, where surgeons opened his chest and ever so gently withdrew the blade.

Ms. Curry was apprehended in the store. “I’ve been after him for six years,” she cried. “I’m glad I done it.”

At her arraignment the next day, The New York Times reported, she was scarcely her own best advocate.

“I understand this is the woman who is accused of stabbing the Reverend Dr. King with a knife,” the judge said.

“No,” Ms. Curry shouted. “It was a letter opener.”

On Oct. 17, 1958, a grand jury indicted her on a charge of attempted first-degree murder. If convicted, she could have gone to prison for 25 years.

But psychiatrists found she had paranoid schizophrenia and an I.Q. of about 70, and she was committed to Matteawan State Hospital for the Criminally Insane, near Poughkeepsie, N.Y. .

She remained there for some 14 years. She was later institutionalized for about a year at the Manhattan Psychiatric Center on Wards Island, in the East River. She lived in a series of residential-care homes before entering the nursing home.

Ms. Curry apparently left no living immediate family. If her body is not claimed in the coming weeks, it will be taken to New York’s potter’s field on Hart Island, in Long Island Sound off the Bronx, her final institutional resting place.

Correction: March 21, 2015 

An earlier picture caption with this obituary misidentified a woman in the photo with Dr. King. She is not Ms. Curry.

CREDIT: NEW YORK TIMES  MARGALIT FOX