WASHINGTON — U.S. Sen. Daniel Inouye of Hawaii, a highly decorated World War II combat veteran who used his status as one of the longest-serving and most powerful Democrats in Washington to funnel billions of dollars to his home islands, died Monday at Walter Reed National Military Medical Center in Bethesda, Md. He was 88.

Peter Boyland, a spokesman for the senator, said the cause was respiratory complications.

Sen. Inouye cut a singular figure in the nation’s capital when he arrived in Washington in 1959 as a representative from the nation’s newest state and the first Japanese-American elected to Congress.

A methodical behind-the-scenes operator who rarely sought the media spotlight, he was little known outside Hawaii and the halls of the Capitol. But his wartime record, for which he received the nation’s highest military award for valor, the Medal of Honor — coupled with his reputation for a bipartisan approach to politics — helped him gain respect and influence from colleagues of both parties in Washington.

After serving in the House, he was elected to the U.S. Senate in 1962 and began a career as Hawaii’s most important patron in Washington. As longtime chairman of the Appropriations defense subcommittee — and since 2009, of the entire Appropriations Committee — Sen. Inouye ensured Hawaii, once a farflung agricultural outpost, received a steady flow of dollars to develop military sites and modern transportation, communication and education systems.

Proudly describing himself as “the No. 1 earmarks guy in the U.S. Congress,” he was — along with his friend and political ally Ted Stevens, the late Republican senator from Alaska — one of the last unapologetic purveyors of political pork.

Sen. Inouye came to national attention only on occasion, most notably when he helped orchestrate inquiries into the Watergate scandal and Iran-Contra affair — two of Congress’s most politically explosive investigations into alleged White House wrongdoings. But he was a towering personality in Hawaii, where had had been born to working-class Japanese immigrants.

He grew up planning to become a doctor until 1942, when as a teenager barely out of high school, he joined what would become a revered Army regiment of Japanese- Americans.

On an Italian battlefield two years later, he destroyed three enemy machine gun nests even as bullets tore through his stomach and legs. A grenade nearly ripped off his right arm, and it was later amputated in an Army hospital.

Back in the United States, the young lieutenant was wearing his empty right sleeve pinned to his officer’s uniform when he stepped into a San Francisco barbershop for a haircut. “We don’t serve Japs here,” the barber told him.

Memories of such encounters remained vivid to Sen. Inouye, who in his political career spoke eloquently in support of civil rights and social welfare programs.

He was one of a number of Hawaiian-born Japanese-American war veterans who returned to the islands to lead a peaceful grass-roots uprising that brought ethnic minorities and working people to power in a place long dominated by white sugar plantation owners.

In 1954, Sen. Inouye was part of a Democratic tide that swept Republicans — who had long run island politics and were closely aligned with sugar interests — out of office. Hawaii has voted solidly Democratic ever since.

His war record and his central role in ushering in that era of social change gave Sen. Inouye “an original power and a kind of aura” that he carried throughout his career, said Neal Milner, a retired political scientist at the University of Hawaii.

“He represents the success of Asian-Americans in Hawaii beginning to throw off the Caucasian elite control that this place had for a long period of time,” Milner said.

In Washington, Sen. Inouye exercised a taciturn authority as a keeper of fading Senate traditions, including collegiality and bipartisan compromise. In 1973, he served on the bipartisan Senate panel that conducted investigative hearings on the Watergate scandal.

The hearings, which gathered reams of evidence about the White House coverup of illegal activities by President Richard Nixon’s reelection campaign, led to the indictment of dozens of administration officials and helped spur Nixon’s resignation in August 1974.

Watched by millions of viewers on network television over the course of three months, the sessions also introduced Sen. Inouye to the public as an undaunted questioner of top White House aides, including H.R. Haldeman and John Ehrlichman.

Ehrlichman’s sworn testimony prompted a rare moment of unguarded emotion from Sen. Inouye: “What a liar!” he whispered into a microphone he mistakenly thought was dead.

The next week, Ehrlichman’s attorney referred to Sen. Inouye as “that little Jap,” prompting a wave of thousands of telegrams and letters in support of the senator.

Sen. Inouye’s widely praised performance won the attention of powerful Democrats including Robert Byrd of West Virginia. As majority leader, Byrd chose Sen. Inouye as the first chairman of the Senate Select Committee on Intelligence, established in 1976 to prevent civil-liberties abuses by U.S. intelligence agencies.

Sen. Inouye was clearly a rising force in his party in 1978, when he was elected party secretary, the third-ranking leadership post among Senate Democrats. He held that position for more than a decade in the 1970s and ’80s and appeared poised to succeed Byrd as Senate majority leader.

Then, in 1987, Sen. Inouye was presented with what was seen as a test of his ability to lead. He was chosen as Senate chairman of Congress’s joint investigation into the Iran-Contra affair. U.S. officials had secretly sold arms to Iran to win the release of U.S. hostages in the Middle East and illegally used some of the profits to support right-wing Nicaraguan rebels known as the contras.

The Iran-contra hearings, which were nationally televised, resulted in the conviction of several ranking government officials but failed to turn up conclusive evidence that President Ronald Reagan had known about the secret deal.

“These hearings will be remembered longest not for the facts they elicited but for the extraordinary and extraordinarily frightening views of the government they have elicited,” Sen. Inouye said in his closing remarks. He called the affair a “chilling” tale of “deceit, duplicity and arrogant disregard of the rule of law.”

While Democrats praised Sen. Inouye for that blunt assessment, many privately criticized him for having mishandled the hearings, permitting the Reagan White House to escape close scrutiny and allowing witnesses — especially Col. Oliver North, who had played a key role in the arms trade — to appear heroic, waxing patriotic about the risks they’d taken to protect America from threats abroad.

When Byrd stepped down as majority leader two years later, Sen. Inouye made a bid to replace him but lost to George Mitchell of Maine.

Daniel Ken Inouye was born Sept. 7, 1924, in Honolulu. He was the oldest of four children and grew up in what he described as “respectable poverty” as his father held two jobs — file clerk by day, waiter by night — to support the family.

One of his most searing childhood memories was the Japanese attack on Pearl Harbor in December 1941. He rushed to tend to the wounded.

“Seventeen years old at the time,” he later wrote in The Washington Post, “I was filled with grief as I came to the realization that the pilots who had dropped the bombs were people who looked like me.”

The U.S. government soon declared Americans of Japanese descent “enemy agents” and sent more than 100,000 to internment camps around the American West.

In 1943, after the government allowed nisei — American citizens born of Japanese immigrants — to join the military, Sen. Inouye quit his premedical studies at the University of Hawaii to sign up with the 442nd Regimental Combat Team, made up entirely of Japanese-Americans.

Sen. Inouye’s military decorations included the Distinguished Service Cross, the Bronze Star Medal and the Purple Heart.

In 2000, Sen. Inouye was one of 22 Asian-American veterans awarded the Medal of Honor after a review of their combat records.

While hospitalized for his war wounds at an Army hospital in Michigan, Sen. Inouye took to playing bridge with a fellow patient — a soldier from Kansas, Bob Dole, who had also been gravely injured in Italy.

When they talked about their futures, Dole said he planned to go to law school, run for the state legislature and eventually win a seat in Congress. Sen. Inouye graduated from the University of Hawaii in 1950 and George Washington University law school in 1952.

He entered the territorial legislature in 1955 and was elected to Congress in 1959 — one year before Dole began his own long Capitol Hill career as a representative and senator.

“I went with the Dole plan,” Sen. Inouye liked to say about his own quick path to Washington politics, “and I beat him!”

Sen. Inouye campaigned on Capitol Hill for national recognition of Japanese-Americans’ sacrifices during the war. He was one of several politicians, including Rep. Norman Mineta, D-Calif., who worked to pass the Civil Liberties Act of 1988, which gave each surviving internee $20,000 in compensation and admitted that the internment had resulted from “race prejudice, war hysteria, and a failure of political leadership.”

As chairman of the Indian Affairs Committee, he was instrumental in passing legislation in 1989 that established the Smithsonian’s National Museum of the American Indian on the Mall. Four years later, he successfully pushed for a formal apology from the federal government for ousting the Hawaiian monarchy in the late 1800s.

His first wife, Margaret Awamura Inouye, died in 2006 after 56 years of marriage. In 2008, he married Irene Hirano, president and chief executive of the Japanese American National Museum in Los Angeles. Besides his wife, survivors include a son from his first marriage, Daniel Inouye Jr.; a stepdaughter, Jennifer Hirano; and a granddaughter.

Widely regarded as a strong and uniting figure, Sen. Inouye was chosen by his fellow Democrats to give the keynote address at the party’s 1968 national convention in Chicago.

It was a period of national unrest following the assassinations of Sen. Robert Kennedy, D-N.Y., and the Rev. Martin Luther King Jr. Speaking not as a Democrat as much as a citizen disturbed by the violence, Sen. Inouye described a troubling “loss of faith” among Americans.

“I do not mean simply a loss of religious faith,” he said. “I mean a loss of faith in our country, its purposes and its institutions. I mean a retreat from the responsibilities of citizenship.”

He then called for Americans to rebuild their trust in government — an extraordinary statement from man whose people had suffered grave injustices at the hands of the government.

Sen. Inouye’s address was immediately overshadowed by the convention’s political infighting and by a violent police crackdown on thousands of antiwar demonstrators in the streets outside.

It was a “remarkable speech,” political journalist Haynes Johnson wrote in The Post in 1996, “that drew little attention then and is even less remembered now.”