Dr. Kurt Isselbacher was 10 years old in July 1936 when he and his parents boarded a ship that would take them to the United States. They were escaping Nazis who had begun attacking their family in Germany, where many relatives who remained behind would perish in the Holocaust.

“I believe medicine became my calling in order to justify my survival, to be of service to others, to provide support and comfort to those in need, and to do it with compassion,’’ he would later write.

In a wide-ranging career, he became a physician and a researcher, an editor of an important textbook and director of the Cancer Center at Massachusetts General Hospital, an academic leader at Harvard Medical School and one of the world’s most prominent gastroenterologists. Dr. Isselbacher, who was still working four days a week at 93, died of a stroke on July 18.

“Not becoming one of the 6 million Jews that were exterminated has had a major impact on how I have conducted myself and how I have viewed people, life, and the world,’’ Dr. Isselbacher wrote in a memoir.

Appointed chief of gastroenterology at MGH when he was 31, he went on to become one of the specialty’s leading figures — making key findings and mentoring dozens of physicians who became top researchers and academicians.

“He made so many discoveries,’’ said Dr. Lawrence S. Friedman, who chairs the department of medicine at Newton-Wellesley Hospital. “He was the chief of gastroenterology at Mass. General, but many people considered him the chief of gastroenterology in the country.’’

Dr. Isselbacher had been a co-editor, and former editor-in-chief, of the respected textbook “Harrison’s Principles of Internal Medicine.’’

And while his scientific influence stretched around the world, Dr. Isselbacher’s legacy was most pronounced at Mass. General. “He truly was one of the giants of this hospital,’’ said Dr. Peter L. Slavin, president of MGH.

By the example of the rigor with which he conducted research, and the high bar he set for himself, Dr. Isselbacher “set the standard of ‘mentor,’ ’’ Dr. Daniel K. Podolsky, president of the University of Texas Southwest Medical Center, wrote in a 90th birthday tribute to Dr. Isselbacher, published in the journal Gastroenterology.

Podolsky, who trained under Dr. Isselbacher, said in that 2015 article that he was also a mentor in “temperament and manner. He is a reassuring presence at the bedside, and with an economy of expression, able to convey to a patient, or trainee, or colleague, that he is truly listening. And there was in his manner something of a sense of the wry and ironic that has only become more refined in the course of time.’’

“His intelligence, his humility, his commitment to patients, and his hunger for coming up with better answers for them was truly inspiring,’’ Slavin said of Dr. Isselbacher. “He also had this incredible twinkle in his eye which really sort of captured his personality, his brilliance, his sparkle, and his impishness.’’

An only child, Kurt J. Isselbacher was born in Wirges, Germany, on Sept. 12, 1925, the son of Albert Isselbacher, who ran clothing stores there and in Portsmouth, N.H., after emigrating, and Flori Strauss, who helped out with the business.

At dawn on Easter morning in 1933, Nazis in Wirges broke into his family’s building, which housed their store, their apartment, and another residence above them. Forcing everyone to stand outside and face the front wall, the Nazis beat Dr. Isselbacher’s father and forced him to pile all their belongings outside, which the Nazis burned while neighbors walked past on their way to church, never intervening.

In a separate incident, a drunken Nazi officer beat Dr. Isselbacher’s paternal grandfather to death. At school, classmates in the Hitler Youth turned on young Kurt. “I was frequently accosted, beaten, and left lying bleeding on the pavement at school,’’ he wrote. “I still have the scars that are visible reminders of my grammar school days.’’

Once the family settled in Portsmouth, Dr. Isselbacher peddled newspapers as a youth to help his family financially. He was also a good student and was accepted at the two schools to which he applied, Dartmouth College and Harvard University. He chose the latter because the student swimming requirement was 50 yards, rather than 200.

Dr. Isselbacher finished his Harvard undergraduate studies in a couple of years and then graduated from Harvard Medical School in 1950. His rise in medicine was steady, and often swift. He served as an officer in the US Public Health Service and did research at the National Institutes of Health.

One day while attending a friend’s wedding, he met Rhoda Solin, a law student. The bride, he wrote, “brought me over to Rhoda’s table and said, “You two better get to know each other because you’re going to get married!’’

He was “entranced by her radiant face and beautiful blonde hair,’’ and he wrote that as they danced, he realized that Rhoda “was different from anyone I had met before.’’

They married in 1955, had four children, and lived in Newton. Mrs. Isselbacher, a prominent lawyer whose work included medical regulatory issues, died in 2015. Their first child, Lisa, died at 41, of cancer, in 1999.

Along with serving as chief of gastroenterology at MGH for more than 30 years, Dr. Isselbacher had been the Mallinckrodt distinguished professor of medicine at Harvard Medical School. In the late 1980s, he set aside leading his MGH department to direct the hospital’s newly established Cancer Center. .

Among the more than 400 papers he published were major breakthroughs that included identifying the enzymatic defect responsible for galactosemia — a disorder that affects the ability to properly metabolize sugar. Other discoveries advanced scientific knowledge of the liver, the intestine, and mutations in the BRCA1 gene in the study of hereditary breast cancer.

The recipient of numerous honors, Dr. Isselbacher had been president of the American Gastroenterological Association, the American Association for the Study of Liver Disease, and the Association of American Physicians, which awarded him the Kober Medal. He also was a fellow of the American Academy of Arts and Sciences.

Two of his three children, who all live in Newton, are physicians — Dr. Eric Isselbacher and Dr. Kate Isselbacher — and the third, Jody Isselbacher, is a lawyer.

A service has been held for Dr. Isselbacher, who also leaves eight grandchildren (two of them physicians) and two great-granddaughters.

Though Dr. Isselbacher was a father figure to generations of gastroenterologists and cancer researchers, his advice and mentoring were sought just as often by his children and grandchildren.

“Every word out of his mouth was so full of wisdom. You just wanted to record it all,’’ Eric said. “He was truly the rock of the family and the source of light, of hope. He energized everybody and beamed goodness around.’’

Even as age left Dr. Isselbacher using two canes to get around, Eric added, “he was always an optimist, finding the best in everything, reassuring people that with hard work and dedication, you’ll be OK. He never gave up.’’

For the 50th anniversary report of his Harvard class, Dr. Isselbacher summed up his life in three sentences of gratitude.

“I have been blessed with a wonderful wife, Rhoda, and family,’’ he wrote. “I have been privileged to obtain fulfillment in medicine and biomedical research throughout my career. I could have asked for no more.’’

Bryan Marquard can be reached at bryan.marquard@globe.com.