US: Daniel Inouye of Hawaii was one of the last World War II heroes in Congress, a loyal voice for minorities and the disenfranchised who eventually became the longest-serving member of the US Senate.
The veteran Democrat, who died from respiratory problems Monday at age 88, voted on some of the most historic US legislation of the last half century including the Civil Rights Act of 1964.
"Tonight, our country has lost a true American hero," President Barack Obama said in a statement.
Inouye, the most senior Asian-American politician in US history and the first Japanese-American to serve in Congress, was chairman of the powerful Senate Appropriations Committee which oversees federal spending.
He had represented Hawaii in Congress from the day the Pacific island chain officially became the 50th US state in 1959.
Elected to the Senate in 1962, Inouye eventually earned the title president pro tempore -- the designation for the chamber's longest-serving member which put him third in line for the US presidency, behind the vice president and speaker of the House of Representatives.
The new "president pro temp" is Patrick Leahy, 72, chairman of the Senate Judiciary Committee but also first in line to succeed Inouye as head of Appropriations.
Inouye has served in the Senate longer than anyone except Robert Byrd, who died in 2010 at age 92, after 51 years in the chamber.
"In Washington, he worked to strengthen our military, forge bipartisan consensus, and hold those of us in government accountable to the people we were elected to serve," Obama said.
"But it was his incredible bravery during World War II -- including one heroic effort that cost him his arm but earned him the Medal of Honor -- that made Danny not just a colleague and a mentor, but someone revered by all of us lucky enough to know him."
Although he gained national recognition for his role on the 1970s Watergate Committee and as chairman of the Iran-Contra Committee in 1987, Inouye spent his career largely out of Washington's bright media glare, instead pressing his case for bipartisan cooperation with quiet determination and grace.
"Though gentle in style, he was a fierce warrior when it came to fighting for his nation or standing up for Hawaii," said Senator Barbara Mikulski, the longest-serving woman in the chamber's history.
Tributes poured in from Republicans including Senate Minority Leader Mitch McConnell, who noted Inouye's status as a veteran of the bombing of Pearl Harbor by Japanese fighter planes.
"An iconic political figure of his beloved Hawaii, and the only original member of a congressional delegation still serving in Congress, he was a man who had every reason to call attention to himself but who never did," McConnell said.
The Japanese government, which bestowed its highest civilian award on Inouye last year, also hailed the late senator.
"He worked to strengthen the unity and the development of the Japanese community in the United States," Japan's top government spokesman Osamu Fujimura said.
"The depth of his achievement cannot be expressed in words."
Much of the institutional fabric of the Senate over the last half-century became a part of the senator from Hawaii.
Inouye was already into his second six-year term in the chamber when its current youngest member Mike Lee was born in 1971.
Inouye's remarkable story as a US Army soldier in World War II continues to inspire. He was one of several Asian-Americans who belatedly received the Medal of Honor in 2000.
According to his biography that accompanied his medal, Inouye led an attack on an enemy position on a ridge near San Terenzo, Italy in April 1945, crawling up a hillside and hurling two grenades into a machine gun nest to neutralize the position.
"Although wounded by a sniper's bullet, he continued to engage other hostile positions at close range until an exploding grenade shattered his right arm," but he continued to direct his platoon until US forces captured the ridge.
Inouye's death leaves Hawaii at a loss in the Senate.
The state's junior Senator Daniel Akaka, just four days younger than Inouye, has served since 1990 and retires on January 3, to be replaced by congresswoman Mazie Hirono, who won election in November.
It was not immediately clear who might fill Inouye's seat, with Hawaii's governor expected to appoint a replacement.
"Tomorrow will be the first day since Hawaii became a state in 1959 that Dan Inouye will not be representing us in Congress," Akaka said Monday.
"Every child born in Hawaii will learn of Dan Inouye, a man who changed the islands forever."
Inouye died at a US military hospital in Washington surrounded by his family, according to his office. His last word was "Aloha."