The Senate lost a World War II combat veteran and Medal of Honor recipient on Monday evening when Hawaii Democrat Daniel K. Inouye died of respiratory complications at the age of 88.

Inouye, the Senate’s most senior senator and the first Japanese-American elected to Congress, won a seat in the chamber in 1962 after serving two House terms as his state’s first congressman following Hawaii’s achievement of statehood.

AP In this May 19, 1973 file photo, Hawaii Sen. Daniel K. Inouye questions a witness during the Watergate hearing on Capitol Hill. Inouye, who played key roles in congressional investigations of the Watergate and Iran-Contra scandals, died of respiratory complications, Monday, Dec. 17, 2012.

At the helm of the powerful Senate Appropriations Committee, a post he accepted in 2009 when West Virginia’s Robert Byrd relinquished that throne, the softspoken senator was notable for his marked divergence from the typical partisanship and his willingness to cooperate with the GOP.

Inouye’s lifelong service to his country began with his enlistment in the Army in 1942, shortly following the attack on Pearl Harbor. He was in the middle of his ninth consecutive term and was the second-longest serving senator in U.S. history, after Byrd, and is one of only five U.S. senators to have represented his state.

Medal of Honor recipient Dan Inouye became the longest-serving senator, having served nine terms after first being elected in 1962. NBC's Brian Williams reports.

His colleagues were quick to honor Inouye. “Tonight, our country has lost a true American hero with the passing of Senator Daniel Inouye,” President Barack Obama said tonight in a statement released by the White House, and Senate Majority Leader Harry Reid paid his respects on the Senate floor. “No one has been a better American than Senator Inouye,” Reid said. “We will all miss him, and that’s a gross understatement.”

He rose to win national esteem during 1973’s Watergate hearings as a leading member of the Senate select committee that investigated the scandal and ultimately led to the resignation of President Richard Nixon in the face of a near-certain vote to impeach him in the House. The respect Inouye won through that endeavor helped land him an appointment as chairman of the special committee investigating the Iran-Contra scandal. His speech upon the conclusion of that panel’s hearings quoted Thomas Jefferson regarding the crucial “spirit of resistance to government.”

“We all knew he would do the moral thing regardless of the consequences - whether it was passing judgment on a President during Watergate or on another President in the Iran Contra hearings,” Vice President Joe Biden said in a statement.

Jim Watson / AFP/Getty Images file US Senator Daniel Inouye, D-HI, introduces retired US General Eric Shenseki during a full committee hearing on Shenseki's nomination to be Veterans Affairs Secretary on Capitol Hill in Washington, DC, January 14, 2009.

After serving two years in the Army at the ripe age of 20, Inouye was wounded in battle and lost his right arm, an incident for which the then-medical student was eventually awarded the Medal of Honor, the nation's highest military award. Over the course of his recovery, he met Bob Dole in a Michigan hospital, an experience Inouye later credited with inspiring his own desire for a career in politics. He then went on to earn a law degree before entering the political arena in 1959.

Inouye’s Army experience led him to concentrate much of his political efforts on defense issues. He voted to repeal the “Don’t Ask, Don’t Tell” policy in 2010, a landmark measure that eventually reversed an almost 20-year-old policy on the service of gay individuals in the military. Though his public words were seldom and few, in 2002 he argued against an assertion by then-President George W. Bush that Democrats were soft on national security. “This is not a time for Democrats and Republicans to say, ‘we got more medals than you, we’ve lost more limbs than you, we’ve shed more blood than you,' Inouye shot back at the time.

Inouye is survived by his wife, Irene Hirano Inouye, his son Daniel Ken Inouye Jr., Ken's wife Jessica, and granddaughter Maggie and step-daughter Jennifer Hirano. He was preceded in death his first wife, Maggie Awamura.