Dr. John S. Najarian, a pioneering transplant surgeon who served for decades as head of surgery at the University of Minnesota and whose career was marked by achievement and controversy, has died.

Najarian died of natural causes Monday night at a memory care center where he lived in Stillwater, his sons Dave and Pete said Tuesday. He was 92.

Najarian leaves a complex legacy. He spearheaded experimental lifesaving transplants for adults and children, and he used his immersive knowledge of immunology and surgery to create a drug called ALG that prevented organ rejection in many people.

Yet the Food and Drug Administration shut down the ALG program at the U in 1992, citing dozens of violations of federal drug-testing rules. For two decades, the university received millions of dollars from improper sales of the drug, according to Star Tribune reporting using public records.

Najarian was later indicted on charges of illegally distributing ALG, costing him his job as chairman of the U’s surgery department. A judge dismissed six of the 21 charges against him and jurors acquitted him of the remaining charges in 1996.

After the courtroom ordeal, Najarian chose to keep operating on patients.

“I think any one of us, going through something like that, would have been extremely bitter,” said Pete Najarian, an options trader who appears frequently on CNBC. “He didn’t ever think about it. Even though he was approached to sue back the university, and others, he just said, ‘Look, I want to get back and start transplanting again. It’s what I do; it’s what I’m good at.’ ”

John Najarian was born in Oakland, Calif., in 1927, the son of Armenian immigrants. After growing up in the Bay Area, he played college football as an offensive tackle for the University of California, Berkeley, joining the team in its 1949 Rose Bowl loss to Northwestern.

“The two weeks leading up to the Rose Bowl were when my med school classmates spent their time studying for finals, which were very important and very difficult in the first year,” Najarian was quoted as saying in Cal Sports Quarterly. “So I went to the Rose Bowl with a suitcase full of books, which I never opened, needless to say.”

He quickly became a successful organ-transplant surgeon and was recruited by many colleges, ultimately choosing the University of Minnesota Department of Surgery, where then-chief of surgery Dr. Owen Wangensteen was building an academic medicine program known internationally for surgical innovation and a tolerance for unconventional approaches.

Najarian took over as head of surgery there in 1967, after Wangensteen retired. He was 39 at the time.

“Already widely known as the founder of one of the nation’s first kidney transplantation services (at the University of California, San Francisco), Najarian had been attracted by the basic science research base at Minnesota,” reported a 2005 article in the Archives of Surgery.

He was known for his dual rigor in both immunological science and surgery, which is what allowed him to innovate.

“John — Dr. Najarian — was equally proficient as a surgeon and as an immunologist. And that was incredibly important. Because he was the one who pushed the boundaries in what you could do with transplant,” said Dr. Jakub Tolar, a bone-marrow transplant doctor who is dean of the U’s Medical School today.

Dr. Sayeed Ikramuddin, the current chair of surgery at the U, said Najarian was known for pioneering islet cell transplants and kidney transplants for diabetes, and pediatric transplants, among many other things.

In 1995, following a series of investigative reports in the Star Tribune, Najarian was indicted on charges of fraud, theft and tax evasion related to allegations that under his watch, the Medical School had taken in millions in illegal profits from sales of ALG, which was unlicensed.

After Najarian was acquitted, the university eventually paid a $32 million settlement to the federal government.

Though no longer head of surgery, Najarian went back to work doing transplants. Dave Najarian said the experience didn’t seem to change his father’s personality.

“He knew he was right,” Dave Najarian said. “He was never yelling about it or making a fuss about it. He was just happy that the drug he developed saved so many lives.”

John Najarian was preceded in death by his wife of 67 years, Mignette, who died last year, and his son Paul, who died in 2014. He’s survived by sons Jon, Dave and Pete, and many grandchildren and great-grandchildren. No services have yet been announced.

Staff Writer Glenn Howatt contributed to this report.