Recurrent prostate cancer hastened his retirement from the Senate in 2015, two years before his second term — the last he pledged to serve — had expired. He had previously fulfilled a campaign promise to serve no more than three terms in the House, arguing that “our founders saw public service and politics as a calling rather than a career.”

AD

AD

Norman J. Ornstein, an American Enterprise Institute congressional scholar, said Dr. Coburn was known primarily for his unwavering commitment to social and fiscal conservatism, particularly his opposition to abortion rights, same-sex marriage, global-warming science and federal government expansion.

In some ways, Dr. Coburn presaged elements of the tea party movement, with its contempt for the Washington establishment. After the movement roared to life in 2009, he expressed admiration but kept his distance, preferring the part of dissident to faction leader. “He didn’t care if he enraged or alienated his fellow Republicans, including the leaders,” Ornstein said. “He held pretty stubbornly to principles.”

Dr. Coburn saw himself as a contrarian who wore his intermittent unpopularity as a badge of honor and grew irascible when others tried to convince him that party loyalty trumped his core beliefs. “I am not a go-along, get-along guy if I think it is the wrong way to go,” he once declared. He developed a reputation for rigorous leadership on matters of congressional oversight, even when it entailed confronting powerful forces in his own party.

AD

AD

“I see them make decisions every day that benefit their career, rather than the country,” he told the CBS program “60 Minutes” in 2014. “And that’s what’s so sickening about Washington. To me, it’s about our future. It’s not about the politicians. And we’ve switched things around where now it’s about the politicians and not the future of the country.”

Dr. Coburn, who once said he was “aloof from the counterculture” and had “never even heard of marijuana” while attending Oklahoma State University in the late 1960s, married his childhood sweetheart (a Sooner State beauty queen), and was a prosperous businessman and physician in Muskogee and deacon in his Southern Baptist church before running for the U.S. House in 1994.

He plunged into the fray on Capitol Hill amid the Republican “revolution” led by Rep. Newt Gingrich (R-Ga.), whose “Contract With America” promised to slash the size of government.

AD

AD

Viewed as an obstructionist even by some Republicans, Dr. Coburn considered himself a fiscal hawk at all costs amid a billowing federal deficit and the growing cost of entitlement programs. “It is evil to spend your kids’ money, spend away their future,” he told The Washington Post. “It is good to be frugal. This is good and evil, black and white.”

He at times grated on senior leaders of both parties with his denunciations of expensive pet projects and earmarks — while also making a distinction between “legitimate” tax breaks for oil and gas companies from his petroleum-producing state and costly “subsidies” for ethanol producers in Iowa.

In the Senate, where he won election to an open seat in 2004, Dr. Coburn was notorious for his procedural objections, becoming one of the most prolific brandishers of “holds” and unrelated amendments to thwart legislation or appropriations that he found objectionable.

AD

AD

He drew the ire of the late senator Ted Stevens (R-Alaska), one of the most veteran legislators in the chamber, when he objected to the allocation of hundreds of millions of dollars for infrastructure projects in the Alaska wilderness widely derided as “bridges to nowhere.” In contrast with some of his colleagues, he did not view such projects as prerogatives of seniority.

He blocked Democratic efforts to fund food safety measures, scholarship grants, home health care for veterans and aid for young victims of the Lord’s Resistance Army in Uganda, saying he would desist when Congress made reductions elsewhere to “stuff that is not working.”

Like the late senator William Proxmire (D-Wis.), who attracted national notice for his Golden Fleece Awards highlighting wasteful and often bizarre federal spending, Dr. Coburn issued an annual “Wastebook” to denounce what he considered abuses of taxpayer money. Among the examples he once highlighted was a $500,000 annual subsidy for a sparsely used Oklahoma airport.

AD

AD

He showed an “iconoclastic streak,” Ornstein said, by embracing concepts poisonous to many in his party: tax increases on the wealthiest earners (to balance the budget) and a respectful working relationship with President Barack Obama, a Democrat and onetime Senate colleague.

Their high-visibility hug in 2009 when Obama delivered an address to Congress surprised many observers. But Dr. Coburn said they had “really hit it off” when they attended Senate orientation together, and he worked with the future president on bills to increase government transparency and accountability. In 2006, they successfully co-sponsored an act to create a searchable central database recording recipients of billions of dollars in federal contracts and grants.

Dr. Coburn supported Sen. John McCain (R-Ariz.) in the 2008 presidential campaign but said he felt a kinship with Obama, who won that race, because he stood by his principles in a city where not all politicians did. McCain died in 2018.

AD

AD

“I’m adamantly against 80 percent of President Obama’s policies,” Dr. Coburn told the Oklahoman newspaper. “But he is an honest liberal. He said he was going to nationalize health care, he said he was going to do all these things. And he’s doing it.”

“Am I to hate him because he has a different viewpoint than I do?” Dr. Coburn continued. “Or should I love him and try to touch his heart and change him?”

Thomas Allen Coburn was born in Casper, Wyo., on March 14, 1948, and grew up in Muskogee, where his father started a company specializing in the processing of optical lenses.

The firm consumed family life, with young Tom Coburn and his siblings working for a quarter an hour sorting bolts, nuts and washers. By the time the future senator was in high school, Coburn Optical Industries had grown into the city’s largest employer.

AD

AD

But his home life was difficult, with an alcoholic father from whom he grew apart. “It was painful, mainly,” he told the Hill, a Capitol Hill publication. “If you see someone you love doing something you know is hurting him, there’s heartache. I’m sure that has a lot to do with my personality today, but I haven’t really been to a shrink to find out what.”

In 1968, he married Carolyn Denton, who had been crowned Miss Oklahoma the previous year. In addition to his wife, survivors include three daughters, operatic soprano Sarah Coburn, Katie Coburn and Callie Coburn; a brother; a sister; and nine grandchildren.

With a single-minded drive for business success, he graduated from Oklahoma State University in 1970 and went to work for Coburn Optical, managing its lens division. His unease around his father led him to open a branch of the company in Virginia, near Richmond.

AD

AD

Revlon, the cosmetics giant, bought the company in 1975, but Dr. Coburn found it hard to disguise his distaste for the new management imported from New York. At the same time, he was diagnosed with advanced melanoma and given a 20 percent chance of survival.

He came through the disease with a life-altering passion for medicine. He graduated from the University of Oklahoma medical school in 1983, established an obstetrics practice in his hometown and spent a decade delivering thousands of babies. (He continued his medical practice while serving in Congress, leading to years of tussling with ethics officials about such outside work, but he said he essentially donated his services by providing them at cost.)

His political ambitions were stoked in the early 1990s when the Muskogee paper quoted the local Democratic congressman, Mike Synar, speaking in favor of nationalized health care. “Somebody’s got to run against this guy,” Dr. Coburn recalled thinking to himself.

The traditionally Democratic district, a swath of northeastern Oklahoma that included Tulsa, was becoming increasingly conservative. Synar, a liberal eight-term veteran of Capitol Hill, was bested in the primary by a retired schoolteacher, and Dr. Coburn won the general election.

Dr. Coburn sought to establish himself in Washington as a voice of moral rectitude. For young staffers, he conducted workshops with graphic slide shows on sexually transmitted diseases. He claimed to speak for his constituents when, amid debates over the 1996 Defense of Marriage Act that defined marriage as a heterosexual union, he declared that “homosexuality is immoral, that it is based on perversion, that it is based on lust.”

He objected to NBC’s decision in 1997 to broadcast the Oscar-winning Holocaust drama “Schindler’s List” during prime time, saying that scenes of nudity, violence and profanity exposed children to “irresponsible sexual behavior.” Amid a torrent of criticism, he apologized to “all those I have offended.”

For all his sharp edges — he was among several junior congressmen who mounted an unsuccessful coup against House Speaker Gingrich in 1997 — Dr. Coburn was regarded as a hard-working and earnest congressman. Because of his self-imposed term limits, he was often placed on committees and panels charged with delivering hard truths and bad news.

In 2010, then-Senate Minority Leader Mitch McConnell (R-Ky.) put him on a federal debt-reduction commission that proposed tax increases. The next year, he and Sen. Carl Levin (D-Mich.) issued a stinging report on the causes of the 2008 financial crisis that accused Goldman Sachs and other powerful interests of deception and greed and also denounced paltry oversight by federal regulators.

While serving as a member on several investigative committees, Dr. Coburn helped lead inquiries into foreign corruption in the United States, corporate tax avoidance and fraudulent Social Security disability claims. He gained the respect of Democratic investigative staff members because he insisted on rigorous probes and was not deterred in questioning witnesses, including major GOP donors.

“Tom Coburn was a terrific oversight partner in the Senate — tough, fearless, and more interested in facts than politics,” Levin said in a statement.

After departing Congress, Dr. Coburn continued to work with public policy groups and other organizations devoted to reducing government. He wrote a book, “Smashing the D.C. Monopoly.” His time in government, he told the Hill, hadn’t taught him anything he didn’t know from his years in business. “Corporate America,” he said, “is often like the federal government — full of power centers that protect the power.”

Tom Hamburger contributed to this report.