Senator Robert Byrd of West Virginia, the longest-serving senator in American history, died Monday at the age of 92, a spokesman for the family said.
Byrd, a Democrat who served in the U.S. Senate since 1959, had been plagued by health problems in recent years and was confined to a wheelchair. He had skipped several votes in Congress in the past months.
Jesse Jacobs, a family spokesman, said Byrd died peacefully at about 3 a.m. at Inova Hospital in Fairfax, Va.
He was the oldest member of the 111th Congress.
The passing of Sen. Byrd will not affect the balance of power in the Senate. West Virginia Governor Joe Manchin, a Democrat, will appoint a replacement senator to serve out the remainder of Byrd's term, which ends in 2012.
Statements from his longtime colleagues poured out Monday morning, as fellow senators remembered Byrd as a steadfast presence in the chamber and a veritable tome of knowledge on how the Senate works.
"The people of West Virginia have lost a dedicated public servant, and America has lost a great defender of its most precious traditions," Senate Majority Leader Harry Reid said in a written statement. "He was the foremost guardian of the Senate's complex rules, procedures and customs, and as leader of both the majority and the minority caucuses in the Senate he knew better than most that legislation is the art of compromise. By virtue of his endurance, Robert Byrd knew and worked with many of the greats of the United States Senate."
President Obama said in a statement that the country has "lost a voice of principle and reason" with Byrd's death.
"He had the courage to stand firm in his principles, but also the courage to change over time," Obama said, in a veiled reference to his controversial past.
Secretary of State Hillary Clinton, a former senator, called Byrd the "heart and soul" of the chamber.
"It is almost impossible to imagine the United States Senate without Robert Byrd," she said.
A traditional black drape has been placed over Byrd's desk, a sign of respect for the deceased in Congress.
The veteran senator held a number of leadership roles during his tenure in the Senate, including conference secretary, majority whip and majority leader -- twice.
Prior to his death, Byrd worked as the president pro tempore -- the second highest ranking official in the Senate and the highest ranking senator in the majority party, putting Byrd third in line to the presidency.
He also served as the senior member of the Senate Appropriations Committee, and the chairman of the Senate Appropriations Subcommittee on Homeland Security. Other committees on which Byrd served were the Senate Budget, Armed Services and Rules and Administration Committees.
Byrd, who never lost an election, cast more than 18,540 roll call votes -- more than any other senator in U.S. history. He had a 98 percent attendance record in his more than five decades of service in the Senate, according to his Web site.
Byrd was born Cornelius Calvin Sale, Jr. in North Wilkesboro, N.C., in 1917. When his mother died in the 1918 flu pandemic, he was sent to live with his aunt and uncle, who renamed him Robert Carlyle Byrd and raised him in the coal-mining region of southern West Virginia.
He received his law degree from American University in 1963, and his undergraduate degree from Marshall University in 1994 -- at age 76.
Byrd was widely regarded as a pre-eminent expert on constitutional law and legislative procedures. Because of his intimate knowledge of Senate rules, he was both feared and respected by his political opponents.
He helped win ratification of the Panama Canal Treaty and was well known for steering federal dollars to his home state. He was also a strong opponent to the Iraq war and vehemently defended minority party rights in the Senate.
He was elected to Congress in 1952, representing West Virginia's 6th Congressional District. Six years later, he was elected to the U.S. Senate.
Byrd threw his support behind Barack Obama a week after the then-senator lost the West Virginia Democratic primary to Hillary Clinton during the 2008 presidential campaign -- an endorsement that symbolized the shift in his views on race.
Once a member of the Klu Klux Klan, it was the defining moment in his lifelong effort to convince the American public of his changed views on race.
"I have done my best to do the right thing," Byrd said during a March 2005 interview with Fox News, during which he was questioned about his KKK membership in the early 1940s.
"The people of West Virginia know that. They know the history. And they put it aside. They continue to return me. I was wrong, as many young men are wrong today, even when they join groups. That's all in the past," Byrd said.
Byrd characterized himself as a "born-again" Christian whose views on race were changed by "time, reflection and the teachings of the Bible."