WASHINGTON (AP) — Senator Robert C. Byrd, a son of West Virginia coal country who used his mastery of Senate rules and a taste for hardball tactics to become a passionate and often feared advocate for the state and the Senate he loved, died Monday at age 92.

The Democrat's 51 years in the Senate made him the longest serving senator in history, while his white mane, stentorian voice and flamboyant speeches citing Roman emperors gave him the presence of a man from a grander, distant time.

In many ways, Byrd embodied the changes the nation has undergone in the past half century. A one-time segregationist and opponent of civil rights legislation, he evolved into a liberal hero as one of the earliest, unrepentant and most vocal foes of the Iraq war and a supporter of the rights of gays to serve in the military. He was the acknowledged Senate Renaissance man, who could recite poetry by memory for hours and yet be ruthless in advancing his legislative agenda — which often involved corralling federal dollars for his perpetually struggling state.

As the Senate opened Monday, Byrd's desk was draped in black cloth with a bowl of white roses. Flags outside the White House and the Capitol flew at half-staff.

Senators who came to the floor to pay tribute recognized both his longevity — he served longer and cast more votes than any senator in history — and the tenacity in which he defended the traditions and prerogatives of the Senate.

"Senator Byrd's ambition was legendary," said Senate Majority Leader Harry Reid, D-Nev., recalling how shortly after he first took his oath of office on January 3, 1959, the same day Alaska became a state, he told a local newspaper that he wanted to someday chair the Senate Appropriations Committee. "Thirty years later, he was — and then lived and served for 21 more."

In many ways a throwback to an era of powerful orators such as Henry Clay or John C. Calhoun, the stiff and formal Byrd could speak at great length with fire and passion, mixing references to the Roman Empire with emotional memories of his almost seven decades with his late wife, Erma.

Brandishing his copy of the U.S. Constitution that he always carried with him, he resisted any attempt to diminish the role of the Senate, as in the days leading up to the 2003 invasion of Iraq when he was one of the few to stand up against ceding war-making powers to President George W. Bush.

Byrd was equally tireless in steering federal dollars to his state, one of the nation's poorest, and his efforts will live on in the many highways and buildings in West Virginia that carry his name.

President Barack Obama said the Senate "has lost a venerable institution, and America has lost a voice of principle and reason."

"He held the deepest respect of members of both parties, and he was generous with his time and advice, something I appreciated greatly as a young senator," Obama said in a statement.

A spokesman for the family, Jesse Jacobs, said that Byrd died at about 3 a.m. at Inova Hospital in Fairfax, Va., where he had been since late last week. Byrd had been in frail health for several years.

Byrd was the Senate's majority leader for six of the 51 years he served there and he was third in the line of succession to the presidency, behind Vice President Joe Biden and House Speaker Nancy Pelosi. In its first order of business Monday, 85-year-old Daniel Inouye, D-Hawaii, now in his eighth term, was sworn in to replace Byrd in the mostly honorary position of president pro tempore of the Senate.

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