Paul D. Laxalt, a Republican governor and two-term senator from Nevada who, as one of Ronald Reagan’s most influential advisers and Capitol Hill allies, was dubbed the president’s “First Friend,” died Aug. 6 at a hospital in Reston, Va. He was 96.

The death was confirmed by Tom Loranger, a family spokesman. Mr. Laxalt suffered a debilitating fall in 2012.

Mr. Laxalt, the son of immigrants, often called himself a “Basque sheepherder’s kid.” That folksy description masked a fierce ambition and political savvy that made him a popular governor in the late 1960s and a national player later in his career.

In 1974, he was the only Republican to win a Senate seat previously held by a Democrat in the post-Watergate anti-GOP wave that year. In Washington, Mr. Laxalt was known primarily as a key opponent of the Panama Canal Treaty and as an early and enthusiastic cheerleader for a potential Reagan presidency. The two men, governors of bordering states, shared a brand of self-reliant, western conservatism.

Mr. Laxalt chaired Reagan’s unsuccessful insurgent campaign in 1976 against President Gerald Ford, a fellow Republican. The morning after former Georgia governor Jimmy Carter beat Ford in the general election, Mr. Laxalt encouraged Reagan to try again for the White House four years later.

Mr. Laxalt went on to chair Reagan’s victorious White House campaigns in 1980 and 1984. Despite his status as a junior senator, he saw his clout rise exponentially through his presence at key White House meetings. Time magazine proclaimed him “suddenly one of the most powerful men in Washington.”

Mr. Laxalt became an indispensable conduit between the White House and Congress. He concerned himself mainly with defense and economic policy, sidestepping wedge social issues and befriending colleagues across the aisle — among them Sen. Edward M. Kennedy (D-Mass.), a regular tennis partner.

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Within the White House, Mr. Laxalt became a gatekeeper to Reagan and a backchannel emissary on delicate matters. He was reportedly tasked with telling James G. Watt, Reagan’s embattled interior secretary, to step down in 1983.

His most dramatic moment on the world stage involved the Reagan administration’s efforts to persuade the corrupt and autocratic Philippine President Ferdinand Marcos to make democratic reforms or step aside.

American support for Marcos tumbled after opposition leader Benigno Aquino Jr. was slain in 1983 after returning to Manila from exile in the United States.

The senator traveled to the Philippine capital in late 1985 to express dismay at the pace of change and the failure to find and try Aquino’s killers. He remained in regular contact as Marcos called a snap election marred by widespread voting fraud and that prompted massive, crippling protests.

In February 1986, Marcos was barricaded in the presidential palace in Manila and asked Mr. Laxalt by phone what he should do.

“Mr. President,” Mr. Laxalt said, “I am not bound by diplomatic restraints. I am talking only for myself. I think you should cut and cut cleanly. I think the time has come.”

To Marcos’s agitation, the comment signaled what Washington expected of him. He ceded power to Aquino’s widow, Corazon, and took asylum in the United States shortly thereafter.

Still basking in favorable attention, Mr. Laxalt announced he would not seek a third Senate term and instead mount a bid for the White House. He billed himself as Reagan’s successor and conservative heir apparent, but he soon withdrew because of lackluster fundraising. He called his bid “the four most miserable months of my life” and, ever the loyal party soldier, co-chaired the successful campaign of Vice President George H.W. Bush.

Paul Dominique Laxalt was born in Reno, Nev., on Aug. 2, 1922. The eldest of six children, he often helped care for his siblings while their father herded sheep in the Nevada mountains.

His interest in public affairs was piqued early on by encounters with politicos who frequented his mother’s restaurant in Carson City, Nevada’s capital.

“Invariably, their attention would fix on Paul, quietly weighing them as equals even then, and one or the other would shake his maned head and waggle his jowls and say, ‘That boy will be governor someday,’ ” his brother Robert Laxalt recalled in his noted 1957 memoir, “Sweet Promised Land.”

Mr. Laxalt served as an Army medic in the Pacific during World War II, then received a law degree from the University of Denver in 1949. Returning to Carson City, he married Jackalyn Ross and went into practice with her father, a prominent Republican who became a federal judge. Mr. Laxalt served as Ormsby County, Nev., district attorney in the early 1950s.

In 1962, he was recruited to run for lieutenant governor on a ticket headed by the former cowboy movie star Rex Bell. When Bell died during the campaign, Mr. Laxalt wisely declined to advance on the ticket and challenge the much-liked Democratic incumbent, Grant Sawyer, in the general election.

Mr. Laxalt won the lieutenant governorship and two years later launched a bid to unseat Democratic Sen. Howard Cannon. Mr. Laxalt positioned himself as the candidate for conservatives, embracing GOP presidential candidate Barry Goldwater and the John Birch Society. He lost by just 84 votes while Goldwater was crushed in a national landslide by President Lyndon B. Johnson.

Mr. Laxalt moderated his views before his next race, in 1966, for the governorship. On an anti-big-government platform, he narrowly defeated Sawyer.

Reagan was elected California governor that same year. They worked together to establish the Tahoe Regional Planning Agency, an interstate commission to safeguard the border-straddling, development-besieged and increasingly polluted Lake Tahoe.

“Here are two conservative Republicans who got together and said, ‘We need a government agency,’ ” said history professor Michael Green of the University of Nevada at Las Vegas. “They pursued it and saved the lake.”

To help fix an ailing economy, Mr. Laxalt encouraged the purchase by Howard Hughes, the reclusive billionaire, of several hotel-casinos in Las Vegas and controversially exempted Hughes from having to appear in person for his gaming licenses, a strict requirement for others.

Mr. Laxalt chose not to run for a second term in 1970 because of personal problems. His wife was struggling with alcoholism, and he had grown distant from his children because of his demanding career. “When my little ones called me ‘Governor,’ I decided I wanted out,” he told the New York Times.

He and his first wife were divorced in 1972. He married Carol Wilson, his former secretary, in 1976. Besides his wife, survivors include six children from his first marriage; a stepdaughter; and 12 grandchildren.

In 1974, Mr. Laxalt ran for an open Senate seat vacated by Democrat Alan Bible and defeated then-Lt. Gov. Harry M. Reid (D) by 624 votes. Reid, later a congressman, succeeded Mr. Laxalt in the Senate and became majority leader.

Mr. Laxalt’s career was not without controversy. In 1983, the McClatchy newspaper chain published a report suggesting federal investigators had been dissuaded by Nevada officials friendly to Mr. Laxalt from investigating alleged organized-crime involvement and profit skimming at Ormsby House, a Carson City hotel-casino the senator co-owned after leaving the governorship.

Mr. Laxalt sued McClatchy for $250 million for libel, prompting a countersuit by the publishing company alleging the senator was seeking to silence the media. Both suits were dropped by 1987 with no admission of wrongdoing, an expeditious end to the episode seen as a way for Mr. Laxalt — who had recently stepped down as general chairman of the Republican Party — to focus on his long-shot presidential bid.

In 1990, Mr. Laxalt founded a lobbying firm whose clients included Sirius XM and the American Gaming Association. His name resurfaced in 2013 when his daughter Michelle publicly acknowledged that her son, Adam, was fathered by then-Sen. Pete Domenici (R-N.M.). She was 24 at the time; Domenici was 46 and married. Adam Laxalt was elected in 2014 as Nevada attorney general.

An astute observer and practitioner of high-level politics, Paul Laxalt was known for his candor in explaining the ways of Washington. “If there is a perception of power,” he once told The Washington Post, pointing to his own career, “that is the greatest power.”