Richard L. Garwin, an architect of America’s hydrogen bomb, who shaped defense policies for postwar governments and laid the groundwork for insights into the structure of the universe as well as for medical and computer marvels, died on Tuesday at his home in Scarsdale, N.Y. He was 97.

His death was confirmed by his son Thomas.

A polymathic physicist and geopolitical thinker, Dr. Garwin was only 23 when he built the world’s first fusion bomb. He later became a science adviser to many presidents, designed Pentagon weapons and satellite reconnaissance systems, argued for a Soviet-American balance of nuclear terror as the best bet for surviving the Cold War, and championed verifiable nuclear arms control agreements.

While his mentor, the Nobel laureate Enrico Fermi, called him “the only true genius I have ever met,” Dr. Garwin was not the father of the hydrogen bomb. The Hungarian-born physicist Edward Teller and the Polish mathematician Stanislaw Ulam, who developed theories for a bomb, may have greater claims to that sobriquet.

In 1951-52, however, Dr. Garwin, at the time an instructor at the University of Chicago and just a summer consultant at the Los Alamos National Laboratory in New Mexico, designed the actual bomb, using the Teller-Ulam ideas. An experimental device code-named Ivy Mike, it was shipped to the Western Pacific and tested on an atoll in the Marshall Islands.

Intended only to prove the fusion concept, the device did not even resemble a bomb. It weighed 82 tons, was undeliverable by airplane and looked like a gigantic thermos bottle. Soviet scientists, who did not test a comparable device until 1955, derisively called it a thermonuclear installation.

But at the Enewetak Atoll on Nov. 1, 1952, it spoke: An all-but-unimaginable fusion of atoms set off a vast, instant flash of blinding light, soundless to distant observers, and a fireball two miles wide with a force 700 times greater than the atomic bomb that destroyed Hiroshima in 1945. Its mushroom cloud soared 25 miles and expanded to 100 miles across.

Because secrecy shrouded the development of America’s thermonuclear weapons programs, Dr. Garwin’s role in creating the first hydrogen bomb was virtually unknown for decades outside a small circle of government defense and intelligence officials. It was Dr. Teller, whose name had long been associated with the bomb, who first publicly credited him.

“The shot was fired almost precisely according to Garwin’s design,” Dr. Teller said in a 1981 statement that acknowledged the crucial role of the young prodigy. Still, that belated recognition got little notice, and Dr. Garwin long remained unknown publicly.

Compared with later thermonuclear weapons, Dr. Garwin’s bomb was crude. Its raw power nonetheless recalled films of the first atomic bomb test in New Mexico in 1945, and the appalled reaction of its creator, J. Robert Oppenheimer, reflecting upon the sacred Hindu text of the Bhagavad Gita: “Now I am become Death, the destroyer of worlds.”

For Dr. Garwin, it was something less.

“I never felt that building the hydrogen bomb was the most important thing in the world, or even in my life at the time,” he told Esquire magazine in 1984. Asked about any feelings of guilt, he said: “I think it would be a better world if the hydrogen bomb had never existed. But I knew the bombs would be used for deterrence.”

A Pivot to I.B.M.

Although the first hydrogen bomb was constructed to his specifications, Dr. Garwin was not even present to witness its detonation at Enewetak. “I’ve never seen a nuclear explosion,” he said in an interview for this obituary in 2018. “I didn’t want to take the time.”

After his success on the hydrogen bomb project, Dr. Garwin said, he found himself at a crossroads in 1952. He could return to the University of Chicago, where he had earned his doctorate under Fermi and was now an assistant professor, with the promise of life at one of the nation’s most prestigious academic institutions.

Or he could accept a far more flexible job at the International Business Machines Corporation. It offered a faculty appointment and use of the Thomas J. Watson Laboratory at Columbia University, with wide freedom to pursue his research interests. It would also let him continue to work as a government consultant at Los Alamos and in Washington.

He chose the I.B.M. deal, and it lasted for four decades, until his retirement.

For I.B.M., Dr. Garwin worked on an endless stream of pure and applied research projects that yielded an astonishing array of patents, scientific papers and technological advances in computers, communications and medicine. His work was crucial in developing magnetic resonance imaging, high-speed laser printers and later touch-screen monitors.

A dedicated maverick, Dr. Garwin worked hard for decades to advance the hunt for gravitational waves — ripples in the fabric of space-time that Einstein had predicted. In 2015, the costly detectors he backed were able to successfully observe the ripples, opening a new window on the universe.

Meantime, Dr. Garwin continued to work for the government, consulting on national defense issues. As an expert on weapons of mass destruction, he helped select priority Soviet targets and led studies on land, sea and air warfare involving nuclear-armed submarines, military and civilian aircraft, and satellite reconnaissance and communication systems. Much of his work continued to be secret, and he remained largely unknown to the public.

He became an adviser to such Presidents as Dwight D. Eisenhower, John F. Kennedy, Lyndon B. Johnson, Richard M. Nixon, Jimmy Carter and Bill Clinton. He also became known as a voice against President Ronald Reagan’s proposals for a space-based missile system, popularly called Star Wars, to defend the nation against nuclear attack. It was never built.

One of Dr. Garwin’s celebrated battles had nothing to do with national defense. In 1970, as a member of Nixon’s science advisory board, he ran afoul of the president’s support for development of the supersonic transport plane. He concluded that the SST would be expensive, noisy, bad for the environment and a commercial dud. Congress dropped its funding. Britain and France subsidized the development of their own SST, the Concorde, but Dr. Garwin’s predictions proved largely correct, and interest faded.

Clashes With Military

A small, professorial man with thinning flyaway hair and a gentle voice more suited to college lectures than a congressional hot seat, Dr. Garwin became an almost legendary figure in the defense establishment, giving speeches, writing articles and testifying before lawmakers on what he called misguided Pentagon choices.

Some of his feuds with the military were bitter and long-running. They included fights over the B-1 bomber, the Trident nuclear submarine and the MX missile system, a network of mobile, land-based intercontinental ballistic missiles that were among the most lethal weapons in history. All eventually joined America’s vast arsenal.

While Dr. Garwin was frustrated by such setbacks, he pressed ahead. His core message was that America should maintain a strategic balance of nuclear power with the Soviet Union. He opposed any weapon or policy that threatened to upset that balance, because, he said, it kept the Russians in check. He liked to say that Moscow was more interested in live Russians than dead Americans.

Dr. Garwin supported reductions of nuclear arsenals, including the 1979 Strategic Arms Limitation Treaty (SALT II), negotiated by President Carter and Leonid Brezhnev, the Soviet premier. But Dr. Garwin insisted that mutually assured destruction was the key to keeping the peace.

In 2021, he joined 700 scientists and engineers, including 21 Nobel laureates, who signed an appeal asking President Joseph R. Biden Jr. to pledge that the United States would never be the first to use nuclear weapons in a conflict. Their letter also called for an end to the American practice of giving the president sole authority to order the use of nuclear weapons; a curb on that authority, they said, would be “an important safeguard against a possible future president who is unstable or who orders a reckless attack.”

The ideas were politically delicate, and Mr. Biden made no such pledge.

Dr. Garwin told Quest magazine in 1981, “The only thing nuclear weapons are good for, and have ever been good for, is massive destruction, and by that threat deterring nuclear attack: If you slap me, I’ll clobber you.”

A Whiz Kid at 5

Richard Lawrence Garwin was born in Cleveland on April 19, 1928, the older of two sons of Robert and Leona (Schwartz) Garwin. His father was a teacher of electronics at a technical high school during the day and a projectionist in a movie theater at night. His mother was a legal secretary. At an early age, Richard, called Dick, showed remarkable intelligence and technical ability. By 5, he was repairing family appliances.

He and his brother, Edward, attended public schools in Cleveland. Dick graduated at 16 from Cleveland Heights High School in 1944 and earned a bachelor’s degree in physics in 1947 from what is now Case Western Reserve University.

In 1947, he married Lois Levy. She died in 2018. In addition to his son Thomas, he is survived by another son, Jeffrey; a daughter, Laura; five grandchildren; and one great-grandchild.

Under Fermi’s tutelage at the University of Chicago, Dr. Garwin earned a master’s degree in 1948 and a doctorate in 1949, scoring the highest marks on doctoral exams ever recorded by the university. He then joined the faculty, but at Fermi’s urging spent his summers at the Los Alamos lab, where his H-bomb work unfolded.

After retiring in 1993, Dr. Garwin chaired the State Department’s Arms Control and Nonproliferation Advisory Board until 2001. He served in 1998 on the Commission to Assess the Ballistic Missile Threat to the United States.

Dr. Garwin’s home in Scarsdale is not far from his longtime base at the I.B.M. Watson Labs, which had moved in 1970 from Columbia University to Yorktown Heights, in Westchester County.

He held faculty appointments at Harvard and Cornell as well as Columbia. He held 47 patents, wrote some 500 scientific research papers and wrote many books, including “Nuclear Weapons and World Politics” (1977, with David C. Gompert and Michael Mandelbaum), and “Megawatts and Megatons: A Turning Point in the Nuclear Age?” (2001, with Georges Charpak).

He was the subject of a biography, “True Genius: The Life and Work of Richard Garwin, the Most Influential Scientist You’ve Never Heard Of” (2017), by Joel N. Shurkin.

His many honors included the 2002 National Medal of Science, the nation’s highest award for science and engineering achievements, given by President George W. Bush, and the Presidential Medal of Freedom, the nation’s highest civilian award, bestowed by President Barack Obama in 2016.

“Ever since he was a Cleveland kid tinkering with his father’s movie projectors, he’s never met a problem he didn’t want to solve,” Mr. Obama said in a lighthearted introduction at the White House. “Reconnaissance satellites, the M.R.I., GPS technology, the touch-screen — all bear his fingerprints. He even patented a mussel washer for shellfish — that I haven’t used. The other stuff I have.”

William J. Broad and Ash Wu contributed reporting.