Within two years, he surpassed his announced five-year goal of making sure more than $1 billion in federal funds was sent back to West Virginia, money used to build highways, bridges, buildings and other facilities, some named after him.
In 2006 and with 64 percent of the vote, Byrd won an unprecedented ninth term in the Senate just months after surpassing South Carolinian Strom Thurmond's record as its longest-serving member. His more than 18,500 roll call votes were another record.
But Byrd also seemed to slow after the death of Erma, his wife of almost 69 years, in 2006. Frail and at times wistful, he used two canes to walk haltingly and needed help from aides to make his way about the Senate. He often hesitated at unscripted moments. By 2009, aides were bringing him to and from the Senate floor in a wheelchair.
Though his hands trembled in later years, Byrd only recently lost his grip on power. Last November he surrendered his chairmanship of the Appropriations Committee.
Byrd's lodestar was protecting the Constitution. He frequently pulled out a dog-eared copy of it from a pocket in one of his trademark three-piece suits. He also defended the Senate in its age-old rivalry with the executive branch, no matter which party held the White House.
Unlike other prominent Senate Democrats such as 2004 presidential nominee John Kerry of Massachusetts, who voted to authorize the war in Iraq, Byrd stood firm in opposition — and felt gratified when public opinion swung behind him.
"The people are becoming more and more aware that we were hoodwinked, that the leaders of this country misrepresented or exaggerated the necessity for invading Iraq," Byrd said.
He cited Iraq when he endorsed then-Sen. Barack Obama for the Democratic presidential nomination in May 2008, calling Obama "a shining young statesman, who possesses the personal temperament and courage necessary to extricate our country from this costly misadventure."
Byrd's accomplishments followed a childhood of poverty in West Virginia, and his success on the national stage came despite a complicated history on racial matters. As a young man, he was a member of the Ku Klux Klan for a brief period, and he joined Southern Democrats in an unsuccessful filibuster against the landmark 1964 Civil Rights Act.
He later apologized for both actions, saying intolerance has no place in America. While supporting later civil rights bills, he opposed busing to integrate schools.
Byrd briefly sought the Democratic presidential nomination in 1976 and later told associates he had once been approached by President Richard M. Nixon, a Republican, about accepting an appointment to the Supreme Court.
But he was a creature — and defender — of Congress across a career that began in 1952 with his election to the House. He served three terms there before winning his Senate seat in 1958, when Dwight D. Eisenhower was in the White House.
He clashed with presidents in both parties and was implacably against proposed balanced budget amendments to the Constitution.
"He is a fierce defender of the Senate and its prerogatives in ways that I think the founding fathers really intended the Senate to be," said one-time rival Kennedy.
In a measure of his tenacity, Byrd took a decade of night courses to earn a law degree in 1963, and completed his long-delayed bachelor's degree at West Virginia's Marshall University in 1994 with correspondence classes.
Byrd was a near-deity in economically struggling West Virginia, to which he delivered countless federally financed projects. Entire government bureaus opened there, including the FBI's repository for computerized fingerprint records. Even the Coast Guard had a facility in the landlocked state. Critics portrayed him as the personification of Congress' thirst for wasteful "pork" spending projects.
Robert Carlyle Byrd was born Nov. 20, 1917, in North Wilkesboro, N.C., as Cornelius Calvin Sale Jr., the youngest of five children.
Before he was 1, his mother died and his father sent him to live with an aunt and uncle, Vlurma and Titus Byrd, who renamed him and moved to the coal-mining town of Stotesbury, W.Va. He didn't learn his original name until he was 16 and his real birthday until he was 54.