On mainland China, news of Dr. Jiang’s death or other references to him were censored, highlighting how he remained a perceived political threat two decades after he came to public attention.

“I’m not a hero,” Dr. Jiang was quoted by the state-run Beijing News in 2013 as describing his SARS disclosures. “All I did was say a few honest things.”

While long out of the public eye and muzzled by Chinese authorities, Dr. Jiang’s defiance took on renewed historical significance during the coronavirus pandemic. Parallels were drawn with Beijing’s early coverups of infection numbers with covid and SARS, or severe acute respiratory syndrome. SARS was blamed for more than 800 deaths before it was mostly contained in 2003.

And in late 2019 — weeks before covid was identified as a global threat — an eye doctor in Wuhan, Li Wenliang, called attention to the emerging “SARS-like” public health crisis. He was hailed on Chinese social media as an heir to Dr. Jiang’s whistleblower legacy. Li died of covid in February 2020, and he was declared among the official “martyrs” for battles against covid.

Dr. Jiang’s challenge against the state over SARS reporting brought mixed responses from leaders. State media called him an “honest doctor” and “SARS hero.” Many Chinese viewed him as a rare risk-taker among the coddled elite, someone willing to put his state-bestowed privileges on the line for his conscience.

At the same time, officials tried to tamp down his growing fame, worried he possibly could use it to question other government narratives. “We have 6 million doctors and health care workers,” Gao Qiang, the No. 2 official at the health ministry told The Washington Post in 2003, “and Jiang Yanyong is one among them.”

The virus first emerged in late 2002 in the southern city of Guangzhou. But Chinese authorities withheld data on its spread until early February 2003. Finally, a text message from public health officials read: “There is a fatal flu in Guangzhou.”

In mid-March, the World Health Organization issued its first warning about the virus, but Chinese media ignored it. Then on April 3, 2003, Health Minister Zhang Wenkang said at a news conference that China was “safe” and that “SARS has been placed under effective control” with just 12 cases reported in Beijing and three deaths.

Dr. Jiang was outraged. Although semiretired, he knew that military hospitals were dealing with a surge in SARS patients — more than 100 cases in Beijing alone. He fired off an email to China Central Television and the Hong Kong-based Phoenix television station accusing Zhang, who was also a military-trained doctor, of hiding the true SARS numbers.

“All doctors and nurses who saw yesterday’s news were furious,” he wrote, accusing Zhang of “abandoning his most basic standard of integrity as a doctor.”

Neither station followed up on Dr. Jiang’s missive. It was leaked to Time magazine, which posted a story on April 8, 2003, under the headline “Beijing’s SARS attack.”

International pressure mounted on China and the WHO questioned if Beijing was concealing the scope of the epidemic. Chinese leadership promptly fired Zhang and Beijing’s mayor, Meng Xuenong, while public health officials moved aggressively to contain the spread.

“I felt I had to reveal what was happening,” Dr. Jiang said, “not just to save China, but to save the world.”

But Dr. Jiang’s rise was soon followed by a hard fall. He crossed a red line in China that few dare, issuing public calls for a reckoning over the 1989 Tiananmen bloodshed. There is no official death toll among the pro-democracy protesters who occupied the square, with estimates running from several hundred to more than 10,000.

Tiananmen remains an untouchable subject in Chinese political and civic life. Dr. Jiang’s position as a Communist Party member and high-ranking military officer gave his comments an added level of concern for leaders.

“Our party must address the mistakes it has made,” said a letter to Communist Party officials by Dr. Jiang, who was on duty at No. 301 Military Hospital in Beijing on the night that tanks rolled into the square. “Anyone whose family members were unjustly killed should voice the same request.”

Dr. Jiang and his wife, Hua Zhongwei, were placed under stretches of house arrest, and Dr. Jiang was taken into custody for more than six weeks of “political indoctrination sessions.” He was banned from speaking with foreign media and blocked from leaving the country. He largely disappeared from public view except for a few state-controlled remarks.

After his detention in 2004, Chinese officials issued a terse statement to The Post, saying that the military has been “helping and educating him.”

Jiang Yanyong was born in Hangzhou on Oct. 4, 1931, and raised in nearby Shanghai in a family whose wealth came from banking. He said he decided to pursue a career in medicine after watching his aunt die of tuberculosis.

He studied at Yenching University in Beijing in the years after Mao Zedong’s communist forces took power in 1949. He received his medical training at Peking Union Medical College and later enlisted in the medical corps of the Chinese military.

Dr. Jiang was posted to 301 Hospital in Beijing in 1957. His family background, however, put him under the grip of Mao’s Cultural Revolution, launched in 1966 against foreign influence and others deemed potential enemies of the state.

Dr. Jiang was labeled a counterrevolutionary because of his father’s banking ties and his family tree. His cousin, Chiang Yan-shih, was a high-ranking official with Mao’s rival, the Kuomintang, whose leaders fled to Taiwan after losing the civil war to the communists.

Dr. Jiang was imprisoned and later exiled to China’s western provinces. He was allowed to return to the No. 301 Hospital in the early 1970s after he was declared “politically rehabilitated.” He retired as chief of surgery shortly before the SARS outbreak but kept ties with the hospital to treat patients and mentor physicians.

In 2007, he was barred from leaving China to receive a human rights award from the New York Academy of Sciences.

In addition to his wife, survivors include a daughter and son.

Late in life, Dr. Jiang had one last tangle with authorities. In 2019, on the 30th anniversary of the Tiananmen bloodshed, he dispatched a letter to Chinese leader Xi Jinping demanding accountability for the events of June 1989. Dr. Jiang was placed back under house arrest.