John H. Tanton, a Michigan ophthalmologist who was the architect of a national anti-immigration movement that found expression in the policies of the administration of President Trump and who was labeled by watchdog groups as a thinly veiled white nationalist, died July 16 at a nursing center in Petoskey, Mich. He was 85.

A death notice placed by his family with Stone Funeral Homes of Petoskey said he died “after a 16-year battle with Parkinson’s disease.”

Dr. Tanton had a 35-year career as an eye doctor and surgeon in Petoskey, a prosperous resort community of about 6,000 on the shore of Lake Michigan.

He was best known for leading nationwide efforts to reduce immigration to the United States, primarily as a way to preserve American culture. He also spearheaded efforts to make English the official language of the United States and to abolish bilingual education.

“He is the most influential unknown man in America,” Linda Chavez, a disaffected associate and a onetime adviser to President Ronald Reagan, told the New York Times in 2011.

As early as the 1950s, Dr. Tanton showed interest in population trends and environmental conservation, later saying, “We have a responsibility to preserve these particular acres, so there will be something left for those who come after us.”

He helped found chapters of the Audubon Society, Sierra Club and Planned Parenthood in northern Michigan and soon focused on population expansion as a far-reaching social problem. He joined the Zero Population Growth organization (now called Population Connection) and was its national president from 1975 to 1977.

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About that time, Dr. Tanton concluded that the best way to hold the line on population was to limit the number immigrants allowed into the United States. He sought to promote his views at Zero Population Growth and the Sierra Club, but both groups were uneasy with his new fixation.

“The whole idea of people trying to hijack an organization to advance their cause was outrageous,” Carl Pope, a onetime executive director of the Sierra Club, told The Washington Post in 2006. “And I found many of the things he had said since I had known him deplorable and unconscionable.”

In 1979, Dr. Tanton established the Federation for American Immigration Reform, ostensibly a moderate, nonpartisan advocacy group.

“We don’t want to project an image of racism, jingoism, xenophobia, chauvinism or isolationism,” he wrote in FAIR’s mission statement. “We plan to make the restriction of immigration a legitimate position for thinking people, and to have FAIR identified in the minds of leaders in the media, academia and government as speaking for a consensus of American thought and opinion.”

He was instrumental in helping create a network of more than a dozen related organizations, which came to include the Center for Immigration Studies, Numbers­USA, the Immigration Reform Law Institute, a journal called the Social Contract Press and a publishing company. The groups, most based in Washington or Northern Virginia, have had an outsize influence on Capitol Hill and in framing the national debate on immigration. Most share a goal of tightening U.S. immigration laws.

In the early 1980s, Dr. Tanton teamed with former senator S.I. Hayakawa (R-Calif.) to organize U.S. English, an effort to fight what Dr. Tanton called the “erosion of the English language” because of a growing number of Spanish-speaking immigrants.

The movement gained momentum and had endorsements from former CBS News anchor Walter Cronkite and writers Saul Bellow and Gore Vidal. Chavez, now a conservative commentator, was president of U.S. English.

The group successfully fought for the passage of a 1986 ballot proposition in California, mandating English as the state’s official language. Other states followed suit.

“The people behind U.S. English and FAIR are a bunch of crazies . . . motivated by xenophobia and probably racism,” Fernando Oaxaca, a Los Angeles radio station owner and Republican who served in the administration of President Gerald R. Ford, told the Los Angeles Times in 1986.

Dr. Tanton projected an image as a soft-spoken small-town physician, but in 1988 a two-year-old internal memorandum was leaked, putting his motivations in a different light. In the memo, he warned of a “Latin onslaught,” the increasing influence of the Catholic Church and a threat to the white majority because of the “greater reproductive powers” of Hispanic immigrants.

“As whites see their power and control over their lives declining, will they simply go quietly into the night?” Dr. Tanton concluded. “Or will there be an explosion?”

Chavez, Cronkite and Bellow severed ties with U.S. English, and Dr. Tanton eventually resigned as the group’s chairman.

“I am not a separatist,” he told the Detroit Free Press in 1989. “I believe in the melting pot. I don’t care what the pigment in your skin is or the slant of your eyes.”

He began to receive greater scrutiny for his leadership, fundraising and connections to extremists. In the 1980s and 1990s, Dr. Tanton’s flagship group, FAIR, received as much as $1.5 million from the Pioneer Fund, a foundation that supported research aimed at showing that black people and other minorities are genetically inferior to whites.

Letters in Dr. Tanton’s archives indicate that he corresponded with Holocaust deniers, a lawyer for the Ku Klux Klan and white nationalists. “I have come to the point of view,” he wrote in 1993 to a fellow supporter of limited immigration, “that for European-American society and culture to persist, it requires a European-American majority and a clear one at that.”

A year later, Dr. Tanton’s company published a translation of a French apocalyptic novel, “The Camp of the Saints,” which describes “swarthy hordes” from India overrunning France and putting French women in brothels. Former Trump White House adviser Stephen K. Bannon has spoken approvingly of the book.

In 2002, the Southern Poverty Law Center, which monitors extremist groups, put Dr. Tanton on the cover of one of its publications, calling him the “puppeteer” of the “organized anti-immigration ‘movement’ in America.” The SPLC designated FAIR and the Center for Immigration Studies as hate groups and later added other organizations founded by Dr. Tanton to the list.

Dr. Tanton denounced the SPLC and other detractors as “special interest groups, driven by the need to scare donors into shelling out more money, resorting to repeated, vicious smears and ad hominem attacks.”

Several early associates broke ranks, including Roger Conner, the first director of FAIR. He told the New York Times in 2011 that Dr. Tanton possessed a quiet charisma “so profound that the people around him disregarded things that we should have called him on.”

Dr. Tanton stepped away from leadership roles at FAIR and other groups in 2011, but they continued to thrive, often under his handpicked successors. In recent years, much of the financial support for his network has come from the Colcom Foundation, which was founded by Cordelia Scaife May, a Pennsylvania heir to the Mellon fortune. Scaife May died in 2005, but according to the Chicago Tribune and other published reports, the foundation continues to fund Dr. Tanton’s organizations, including more than $70 million between 2010 and 2015.

Restrictive immigration policies advocated by Dr. Tanton, including the elimination of birthright citizenship granted to U.S.-born children of noncitizens, have found favor in the Trump administration. Several people connected to his organizations have had prominent roles in the government.

Former FAIR executive director Julie Kirchner is the ombudsman of U.S. Citizenship and Immigration Services. Kris Kobach, a former Kansas secretary of state and vice chair of the short-lived White House Commission on Election Integrity, was counsel for FAIR’s legal arm, the Immigration Reform Law Institute. White House counselor Kelly­anne Conway did polling for FAIR and other groups founded by Dr. Tanton.

John Hamilton Tanton was born Feb. 23, 1934, in Detroit. His father was a Canadian immigrant. In the mid-1940s, the family moved to a farm in Sebewaing, Mich.

Dr. Tanton graduated from Michigan State University in 1956 and from the University of Michigan medical school in 1960. After a medical residency in Denver, he settled in Petoskey in 1964.

He rose at 4 a.m. every day, was a beekeeper and taught himself to read German and play piano. Survivors include his wife of 61 years, the former Mary Lou Brown of Petoskey; two daughters; a sister; and two grandchildren.

About half of Dr. Tanton’s archives at the University of Michigan are under seal until 2035. In 2016, Hassan Ahmad, an immigration lawyer in Northern Virginia, filed suit to have the documents released, arguing that they are public records of importance to the nation’s civic discourse.

Ahmad won a legal victory in a Michigan appeals court in June, but a final ruling has not been made. After reviewing thousands of documents in Dr. Tanton’s archives, Ahmad said in an interview, “I think he’s the architect, the mastermind of an effort to push a vile and white nationalist agenda, and I don’t use those terms lightly.”

In addition to Conner and Chavez, another former associate who turned against Dr. Tanton was Patrick Burns, FAIR’s former deputy director.

“It’s sad,” Burns told the Detroit News in 2017. “It’s like a dead cat in a well. It poisons a lot of good water. Tanton has been that cat for 30 years.”