Sen. Daniel Inouye of Hawaii died Monday in Washington, Hawaii News Now reports. He was 88.

Inouye, a Democrat and World War II hero, was a dominant figure in Hawaii politics ever since statehood. He had been hospitalized at the George Washington University Hospital since Dec. 6, when he fainted in his office at the Capitol. He was transferred to Walter Reed Army Medical Center Dec. 9 so doctors could monitor his oxygen intake.

His death was confirmed by Peter Boylan, the senator's deputy chief of staff.

Inouye was the second longest-serving senator in United States history and had already said he intended to run for an unprecedented tenth term in 2016, when he would have been 92.

Inouye succeeded Sen. Robert Byrd, D-W.Va., as president pro tempore of the Senate – third in line for the presidency -- on his death in 2010. He would have succeeded Byrd as the longest serving senator in history on June 29, 2014, which would have been his 18,805th day in office.

Sen. Patrick Leahy, D-Vt., as the senior member of the Senate majority, now becomes president pro tem. Hawaii Gov. Neil Abercrombie, a Democrat, will appoint a successor who will serve until a special election to fill the rest of Inouye's term. The state's other senator, Daniel Akaka, who is also 88, retired this election and will be succeeded by Rep. Mazie Hirono in January.