The Roslin Institute, a research center near Edinburgh where Dr. Wilmut had worked for decades, announced the death in a statement. He revealed in an interview five years ago that he had been diagnosed with Parkinson’s disease, adding that although the Dolly breakthrough would accelerate medical research, “people like me will probably have died of Parkinson’s disease before the new treatments become available.”

In 1986, Dr. Wilmut, then a researcher at the Animal Breeding Research Station — a facility that would later become the Roslin Institute — was in Ireland for a conference when he overheard a conversation in a Dublin bar that would change his life and with it the study of biology.

He heard attendees discussing a Danish scientist who had produced live calves by removing the nucleus from an unfertilized egg and inserting in its place the nucleus from an early embryo, or fertilized egg.

The work had not been published, but Dr. Wilmut realized right away where it might lead. If the method worked, he could create calves and furnish them with disease-resistant genes, a significant breakthrough in farming.

Moreover, the work would overthrow a major tenet of biology ― that development is a one-way street in which the cells of the embryo only move forward, becoming blood, skin, brain, or any of the other 200 specific cell types in the body.

For years, Dr. Wilmut worked closely on the cloning project with colleague Keith Campbell and more than a half-dozen other staff at his research station.

“It had always been said that cloning was impossible to do in mammals, but I didn’t believe it,” Campbell told an interviewer in 2008, four years before his death. Campbell provided a key insight that made cloning possible, observing that in order to work, the timing of cell division had to be aligned in both the donor and recipient cells.

Later accounts often glossed over the fact that Dolly’s cloning was anything but easy.

“The original creation of Dolly the Sheep was like a Hail Mary pass,” said Eric Green, a biologist and director of the Bethesda, Md.-based National Human Genome Research Institute who befriended Dr. Wilmut more than 20 years ago. “It [took] an inordinate number of failures, and then it just worked.”

Dr. Wilmut and his colleagues cloned 277 embryos, but only 13 developed sufficiently to be implanted in surrogate mothers; only one became pregnant. For weeks, researchers slept near the lone pregnant sheep, ready to call a veterinarian if a problem arose, Dr. Wilmut said in 2008.

On July 5, 1996, the first cloned mammal, a Finn-Dorset sheep weighing 14.5 pounds, was born. Cloned from a cell in the mammary gland, the lamb was named Dolly, after the buxom American singer Dolly Parton. Dr. Wilmut and Campbell made sure the animal was healthy, before announcing the historic birth to the world in February 1997.

“Cloned Sheep in Nazi Storm,” “The Clone Rangers Need to be Stopped” and “Golly, Dolly! It’s the Abolition of Man” were just some the alarmist headlines that appeared, recalled Roger Highfield, who co-wrote the 2007 book “After Dolly: The Promise and Perils of Human Cloning,” with Dr. Wilmut, and now serves as science director of the Science Museum Group in England.

In the midst of a media maelstrom, Dr. Wilmut made an unlikely spokesman.

“I think the media were expecting this wild-eyed Dr. Frankenstein type,” Highfield said. “But he was a mild-mannered sort of chap who liked nursing a single malt whiskey at night.”

Dr. Wilmut’s goal in cloning Dolly had been to devise a method of genetically manipulating farm animals, but the uproar over Dolly focused on the one possible application he cared least about: reproductive cloning. Despite his discomfort in the spotlight, Dr. Wilmut worked tirelessly to explain why human cloning was unethical and should not be attempted.

Apart from the ethical reasons, the sheer number of embryos it had taken to obtain a single viable clone made the process wildly inefficient. Cloning also resulted in defects to the animals. Even “Dolly was not a healthy animal,” Green said. She had arthritis and died in 2003 at the age of 6.

Less noted, but more enduring, was Dolly’s contribution to our understanding of development in mammals.

“That showed the arrow of time is not irreversible in development,” James Thomson, a University of Wisconsin at Madison scientist, told the Milwaukee Journal Sentinel in 2008. A cell could be induced to go back to its earliest embryonic state. Thomson would ignite a controversy of his own in 1998, becoming the first to isolate and grow human embryonic stem cells.

The cloning of Dolly left a lasting impression on many scientists, including Thomson and Shinya Yamanaka, a Japanese scientist who in 2006 developed an alternative method of reprogramming cells that did not involve the destruction of an embryo.

Using a virus to deliver four genes into the connective tissue cell of a mouse, Yamanaka turned the cell into the equivalent of an embryonic stem cell, an achievement for which he shared the 2012 Nobel Prize in physiology or medicine.

Researchers are still seeking to make reprogrammed cells that are safe to be implanted in people as blood, brain or other cells, potentially opening up a broad new avenue of medical treatments.

Dr. Wilmut said he had predicted Yamanaka’s discovery almost a decade before it occurred, telling an audience during a slide presentation in Washington that scientists will find a way to put key factors into cells and reprogram them.

“I’ve still got the slide,” he told the Journal Sentinel.

Ian Wilmut was born on July 7, 1944, in the village of Hampton Lucy, England, near Stratford-upon-Avon. His parents were both teachers.

His family moved to Yorkshire, where he discovered an interest in biology as a schoolboy. At the University of Nottingham, he received a degree in agricultural science in 1967. That same year he married Vivienne Craven. They had three children and remained together until her death in 2015.

In 2017, he married Sara Haddon. In addition to his wife, survivors include three children from his first marriage; and five grandchildren.

In 1971, Dr. Wilmut received a doctorate from the University of Cambridge (Darwin College), where he worked in a group studying methods of preserving semen and embryos though freezing. His doctoral thesis was titled “Deep Freeze Preservation of Boar Semen.”

He joined the Animal Breeding Research Station in 1973; it became the Roslin Institute in 1993.

Following the cloning of Dolly, Dr. Wilmut and colleagues cloned a Poll Dorset sheep named Polly, engineering it with the human gene for a blood clotting factor that is missing from people with hemophilia.

In 2002, Dr. Wilmut was made a fellow of the Royal Society and, in 2005, he became the chair of reproductive science at the University of Edinburgh. He was knighted in 2007.

In addition to his scientific papers in Nature, Science and other journals, Dr. Wilmut co-wrote the book with Highfield and another with Campbell and Colin Tudge, “The Second Creation: Dolly and the Age of Biological Control” (2000).

A year before the furor over Dolly, Dr. Wilmut and Campbell had announced the cloning of two Welsh Mountain sheep, Megan and Morag, which the scientists considered the real breakthrough showing that cloning was possible.

But the implanted cells in Megan and Morag were less mature than those used in Dolly. The two Welsh Mountain sheep made the front page of the Daily Telegraph newspaper in England, but failed to make much of a splash beyond that, said Highfield, adding, “Maybe it’s the old cliché that you need to tell the world’s media twice before they know it’s a huge story.”