Tributes are pouring in after the family of former U.S. Sen. Arlen Specter of Pennsylvania announced his death on Sunday. Specter, a Republican for decades until 2009 when he switched to the Democratic Party, is being remembered as a fighter to whom people mattered more than politics.

Specter, who died of complications from non-Hodgkin's lymphoma at his home in Philadelphia on Sunday, "was always a fighter," President Barack Obama said in a statement, of Pennsylvania's longest-serving U.S. senator.

Specter's funeral has been scheduled for Tuesday in Penn Valley, Pa., and will be attended by Vice President Joe Biden, according to the White House. The funeral will be followed by burial in Huntingdon Valley, Pa.

"From his days stamping out corruption as a prosecutor in Philadelphia to his three decades of service in the Senate, Arlen was fiercely independent -- never putting party or ideology ahead of the people he was chosen to serve," Obama said.

Specter, politically moderate, was 82. He was born in Wichita, Kansas, to emigrant Russian Jewish parents. He left Kansas for college, graduating from the University of Pennsylvania in 1951 and Yale law school in 1956. He also served in the Air Force from 1951 to 1953.

Former President George W. Bush remembered him for the integrity with which he "loved our country and served it" for three decades in the Senate. "Laura and I appreciate his contributions to America and are grateful for his many years of public service," Bush said.

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In 2001, Specter voted for Bush's package of tax cuts, but also voted with Democrats to route $450 billion into education and debt reduction.

As a member of the Warren Commission, Specter developed the single-bullet theory in President John F. Kennedy's assassination. Pat Toomey, the Republican who now holds Specter's old Senate seat, said Specter was "a man of sharp intelligence and dogged determination."

Senate Minority Leader Mitch McConnell, a Republican, called Specter a "legendary figure in his beloved Pennsylvania" who "brought his fierce intellect and a prosecutor's drive to countless battles in the Senate." He was "a fighter to the end."

Former Republican presidential candidate and former U.S. Sen. Rick Santorum from Pa. said he served with Specter for more than a decade, and "can say without a shadow of a doubt that he was a fighter, and his commitment to public service was admirable."

G. Terry Madonna, director of the Franklin & Marshall College Poll and professor of public affairs at Franklin & Marshall College, said Specter was an "unusual politician." "He didn't look at polls. He didn't track how his comments were playing out in the press. ... He was fundamentally a pragmatist who could bend with the times."

Former Gov. Ed Rendell, a Democrat, called him "a mentor, colleague and a political institution" who "did more for the people of Pennsylvania over his more than 30-year career with the possible exception of Benjamin Franklin."