Herbert Stempel, the Bronx-born brainiac who became a central figure and whistleblower in the game show rigging scandals of the 1950s, a cultural turning point later chronicled in the 1994 movie “Quiz Show,” died April 7 at a nursing home in New York City. He was 93.

His former wife Ethel Stempel did not give a precise cause but confirmed the death, which was not publicly announced and was first reported on Sunday by the New York Times.

Mr. Stempel, once dubbed a “high-strung Human Univac” after the 1950s supercomputer, displayed an uncanny intelligence and viselike memory from his earliest years. Raised by a widowed mother during the Great Depression, he spent long hours at New York City libraries and showed particular aptitude for geography and history. As a boy, he participated in radio quiz shows.

“When I was a kid,” he later joked, “someone said, ‘If you ask Herb who built the great pyramids, he’ll say, “Do you mean day shift or night shift?” ’ ”

By age 29, he was an Army veteran attending the City College of New York on the G.I. Bill and struggling to support his wife and toddler son. He thought he found a solution to his financial strains when, on Sept. 12, 1956, he watched the premiere episode of the NBC game show “Twenty-One.”

He quickly sent off a note introducing himself to the show’s producers. “I have thousands of odd and obscure facts,” he wrote, “and many facets of general information at my fingertips.”

Producer Dan Enright and host Jack Barry agreed to test Mr. Stempel’s knowledge and found that he scored better than any previous applicant. Enright soon made Mr. Stempel a proposition: “How would you like to win $25,000?”

The offer, however, hinged on Mr. Stempel’s willingness to obey instructions about how the game could be conducted.

“I had been a poor boy all my life, and I was sort of overjoyed,” he would later tell a congressional panel investigating game shows in 1959, “and I took it for granted this was the way things were run on these programs.”

Inspired by the card game blackjack, “Twenty-One” featured two contestants who sat in isolation booths and were required to answer questions of increasing difficulty in an effort to win 21 points. The debut episode was a ratings dud, and sponsors demanded rapid improvement.

The producers decided to ramp up drama by treating the contestants as characters and turning their interactions into a tightly choreographed soap opera. The result was a television tour de force that battled radio programs, newspapers and magazines for commercial and cultural influence at the dawn of the TV age.

“I was assigned to play the role of a nerd, a human computer,” Mr. Stempel told The Washington Post in 1994.

Enright instructed Mr. Stempel to cut his hair short, and the producer handpicked an ill-fitting suit for him. Mr. Stempel was told never to call Barry by his first name, as other contestants did, but rather to address him as “Mr. Barry.” The intent was to create a wooden, unlikable character who would provide a foil for the more attractive contestants. Years later, Enright told PBS that viewers would watch Mr. Stempel and “pray for his opponent to win.”

“He was the antithesis of the image he presented on the air,” said Steve Beverly, a professor of broadcast journalism at Union University in Jackson, Tenn., and an authority on game show history. Beverly said Mr. Stempel’s on-air personality was “almost a cartoon character.”

The coaching, Mr. Stempel discovered, included orders on which questions to answer correctly and which ones to miss. “Everything was explicit,” he told the congressional panel.

Enright, he said, “showed me how to bite my lip to show extreme tension. How to mop my brow. He told me specifically not to smear my brow, but rather to pat for optimum effect, as that created a more tense atmosphere. He told me how to breathe heavily into the microphone and sigh.”

Mr. Stempel’s dominant — and preordained — run on the show lasted from Oct. 17 to Dec. 5, 1956. He was dethroned by Charles Van Doren, the telegenic and suave son of an intellectually prominent family who at the time was a novice English instructor at Columbia University.

“Once I saw him,” Mr. Stempel told the Los Angeles Times decades later, “I knew my days on the show were numbered. He was tall, thin and WASPY, and I was this Bronx Jewish kid. It was as simple as that.”

Mr. Stempel collected nearly $50,000 before he said he deliberately flubbed a question about the winner of the Oscar for best motion picture of 1955. He said “On the Waterfront” — the winner for 1954 — when the correct answer was “Marty.” (Mr. Stempel had seen “Marty” three times.)

Mr. Stempel said he agreed to the defeat because Enright had offered him future television work. When those opportunities failed to materialize, Mr. Stempel decided to expose the rigging. In February 1957, he gave his story to the New York Post, but he said the newspaper decided against running an article to avoid a potential libel suit.

Public revelation of quiz show deception did not begin until 1958, when a standby contestant on the NBC game show “Dotto” found another contestant’s notebook that contained questions and answers for upcoming episodes. Investigations — including New York grand jury proceedings and the congressional inquiry — ensued, and several quiz programs were canceled.

Van Doren pleaded guilty to misdemeanor perjury in 1962, admitting he lied to a grand jury about “Twenty-One.” His sentence was suspended, sparing him jail time.

The scandal became international news. At a news conference, President Dwight D. Eisenhower noted “the general reaction of almost bewilderment that people could conspire to confuse and deceive the American people.” The prominent TV critic John Crosby wrote at the time, “The moral squalor of the quiz show mess reaches through the whole industry.”

The “Twenty-One” affair was revived for a later generation in director Robert Redford’s movie “Quiz Show,” starring Ralph ­Fiennes as Van Doren and John Turturro as Mr. Stempel.

“I wouldn’t call him a saint or a sinner,” TV historian Wesley Hyatt said of Mr. Stempel. “More than anything else, he was just a human being who was caught in a situation that was unprecedented. He did some wise things, and he did some not-so-wise things.”

Herbert Milton Stempel was born Dec. 19, 1926, in the Bronx. He was 7 when his father, a postal carrier, died; his mother raised Herbert and his older sister largely on public assistance.

His first wife, the former Tobie Mantell, died in 1980, and his marriage to Ethel Feinblum ended in divorce. Mr. Stempel had a son from his first marriage, Harvey, who survives him. Additional information on survivors was not immediately available.

After the scandal, Mr. Stempel told The Post in 1994, he lost his game show winnings to a Florida con artist running an off-track-betting scheme. He bounced around jobs and eventually became a researcher in the New York City transportation department.

Unlike Van Doren, who found work at Encyclopaedia Britannica and avoided the public spotlight before his death in 2019, Mr. Stempel was a garrulous presence in documentaries about the quiz show era. He also was a consultant on the Redford movie, reportedly receiving $30,000 for his services.

He long insisted that he was not bitter about his curtailed TV career — or personally angry at Van Doren. Before the men met for the first time, Mr. Stempel was told that he would lose and the manner in which it would happen.

On the day of their final appearance together on “Twenty-One,” Mr. Stempel later recalled, he was frustrated by promotions for that night’s episode. “Every few minutes,” he said, “an announcement would break in saying, ‘Is Herb Stempel going to win over $100,000 tonight?’ and I said, ‘No, he is not going to win $100,000. He’s going to take a dive.’ ”

Harrison Smith contributed to this report.