Byrds death forced politicians and Wall Street bankers to recalculate whether President Barack Obama had enough votes without him to pass a landmark financial regulation bill.
The Democrats now appear to be at least two short of the 60 votes needed to ensure Senate passage, but they are expected to eventually secure the needed backing.
In the early 1940s, Byrd belonged to the racist Ku Klux Klan, a membership he attributed to youthful indiscretion. In Congress, Byrd once denounced civil rights leader Martin Luther King as a self-seeking rabble rouser.
But he had a change of heart, in part caused by the death of a grandson in 1982, and evolved into a leading advocate of equal rights. A few years ago, he helped secure funding for a memorial for King in the nations capital.
First elected to the House of Representatives in 1952 and then the Senate in 1958, Byrd kept a copy of the U.S. Constitution in his breast pocket.
Lord, we appreciate his wit and wisdom, his stories and music, as well as his indefatigable commitment to the principles of freedom that make America great, said Senate Chaplin Barry Black.
As the president pro tempore of the Senate, Byrd was third in line of succession if the president died, after Vice President Joe Biden and House of Representatives Speaker Nancy Pelosi.
Byrds former colleagues expressed condolences and swapped stories.
He once came up to me and asked, Alan, do our colleagues fear me or respect me, former Republican Senator Alan Simpson recalled. I said, They are in awe of you.
In West Virginia, Byrd was revered for his ability to deliver federal dollars to his poor state to build roads, schools and hospitals. Critics called him the Prince of Pork but constituents crowned him as West Virginian of the 20th Century.
Byrds body will be flown to Charleston, West Virginia, for a memorial service on Friday at the state Capitol, with guests to include Obama, Biden and congressional leaders. Both the president and vice president were expected to speak at the memorial service.
The funeral will take place on Tuesday in Arlington, Virginia, and Byrd will be laid to rest at a Virginia cemetery alongside his wife Erma, who died in 2006. The couple will be reburied in West Virginia once a final site is determined.
Editing by Alistair Bell and Vicki Allen source