Former U.S. Sen. Arlen Specter, the outspoken Pennsylvania centrist whose switch from Republican to Democrat ended a 30-year career in which he played a pivotal role in several Supreme Court nominations, died on Sunday. He was 82.

Specter, who announced in late August that he was battling cancer, died at his home in Philadelphia from complications of non-Hodgkins lymphoma, said his son Shanin. Over the years, Arlen Specter had fought two previous bouts with Hodgkin's disease, overcome a brain tumor and survived cardiac arrest following bypass surgery.

Specter rose to prominence in the 1960s as an aggressive Philadelphia prosecutor and as an assistant counsel to the Warren Commission, developing the single-bullet theory that posited just one bullet struck both President Kennedy and Texas Gov. John Connally. The theory remains controversial and was the focus of Oliver Stone's 1991 movie "JFK."

In 1987, Specter helped thwart the Supreme Court nomination of former federal appeals Judge Robert H. Bork - earning him conservative enemies who still bitterly refer to such rejections as being "borked."

But four years later, Specter was criticized by liberals for his tough questioning of Anita Hill at Clarence Thomas' Supreme Court nomination hearings and for accusing her of committing "flat-out perjury." The nationally televised interrogation incensed women's groups and nearly cost him his seat in 1992.

Specter, who had battled cancer, was Pennsylvania's longest-serving senator when Democrats picked then-U.S. Rep. Joe Sestak over him in the 2010 primary, despite Specter's endorsements by President Barack Obama and other Democratic leaders. Sestak lost Specter's seat to conservative Republican Rep. Pat Toomey by 2 percentage points.

A political moderate, Specter was swept into the Senate in the Reagan landslide of 1980.

He took credit for helping to defeat President Clinton's national health care plan - the complexities of which he highlighted in a gigantic chart that hung on his office wall for years afterward - and helped lead the investigation into Gulf War syndrome. Following the Iran-Contra scandal, he pushed legislation that created the inspectors general of the CIA.

As a senior member of the powerful Appropriations Committee, Specter pushed for increased funding for stem-cell research, breast cancer and Alzheimer's disease, and supported several labor-backed initiatives in a GOP-led Congress. He also doggedly sought federal funds for local projects in his home state.

The former Democrat was not shy about bucking fellow Republicans.

In 1995, he launched a presidential bid, denouncing religious conservatives as the "fringe" that plays too large a role in setting the party's agenda. Specter, who was Jewish, bowed out before the first primary because of lackluster fundraising.

Despite his tireless campaigning, Specter's irascible independence caught up with him in 2004. Specter barely survived a GOP primary challenge by Toomey by 17,000 votes of more than 1.4 million cast. He went on to easily win the general election with the help of organized labor, a traditionally Democratic constituency.

Specter startled fellow senators in April 2009 when he announced he was switching to the Democratic side, saying he found himself "increasingly at odds with the Republican philosophy." Earlier in the year, he had been one of only three Republicans in Congress - and the only one facing re-election in 2010 - who voted for President Barack Obama's economic stimulus bill.

He also said he had concluded that his chance of defeating a GOP challenger in the 2010 party primary was bleak. But he said the Democrats couldn't count on him to be "an automatic 60th vote" to give the party a filibuster-proof majority.

Specter outspent Sestak, a retired Navy vice admiral, but Sestak attacked him as a political opportunist who switched parties to save his job. A memorable campaign ad used Specter's own words against him: "My change in party will enable me to be re-elected."

Specter was diagnosed in February 2005 with stage IV Hodgkin's disease, a cancer of the lymphatic system. Announcing the diagnosis with his trademark doggedness, Specter said: "I have beaten a brain tumor, bypass heart surgery and many tough political opponents and I'm going to beat this, too."

He wrote of his struggle in a 2008 book, "Never Give In: Battling Cancer in the Senate," saying he wanted to let others facing similar crises "ought to know they are not alone."

Cancer handed him "a stark look at mortality" and an "added sense of humility," Specter told The Associated Press.

Intellectual and stubborn, Specter played squash nearly every day into his mid-70s and liked to unwind with a martini or two at night. He took the lead on a wide spectrum of issues and was no stranger to controversy.

Born in Wichita, Kan., on Feb. 12, 1930, Specter spent summers toiling in his father's junkyard in Russell, Kan., where he knew another future senator - Bob Dole. The junkyard thrived during World War II, allowing Specter's father to send his four children to college.

Specter left Kansas for college in 1947 because the University of Kansas, where his best friends were headed, did not have Jewish fraternities. He graduated from the University of Pennsylvania in 1951 and Yale law school in 1956. He served in the Air Force from 1951 to 1953.

Friends say his childhood circumstances made him determined, tough and independent-minded. Specter considered his father's triumphs the embodiment of the American dream, a fulfillment that friends say drove him to a career in public life.

He entered politics as a Democrat in Philadelphia in the early 1960s, when he was an assistant district attorney who sent six Teamsters officials to jail for union corruption.

After working on the Warren Commission, he returned to Philadelphia and challenged his boss, James Crumlish, for district attorney in 1965. Specter ran as a Republican and was derided by Crumlish as "Benedict Arlen." But Crumlish lost to his protege by 36,000 votes.

It was to be the last time until 1980 that Specter would win an election to higher office, despite three attempts - a 1967 bid for Philadelphia mayor, a 1976 loss to John Heinz for Senate and a 1978 defeat by Dick Thornburgh for governor.

Specter lost re-election as district attorney in 1973 and went into private practice. Among his most notorious clients as a private attorney was Ira Einhorn, a Philadelphia counterculture celebrity who killed his girlfriend in 1977.

Finally, in 1980, Specter won the Senate seat vacated by retiring Republican Richard Schweiker, defeating former Pittsburgh Mayor Pete Flaherty.

After leaving the Senate in January 2011, the University of Pennsylvania Law School announced Specter would teach a course about Congress' relationship with the Supreme Court, and Maryland Public Television launched a political-affairs show hosted by the former senator.

A funeral was scheduled for Tuesday in Penn Valley, Pa., and will be open to the public, followed by burial in Huntingdon Valley, Pa.

He is survived by his wife, Joan, and two sons, Shanin and Steve, and four granddaughters.

Obama: Specter was 'a fighter'

In a statement released in response to Specter's passing, U.S. President Barack Obama called the former Senator "a fighter," saying that 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."

"He brought that same toughness and determination to his personal struggles, using his own story to inspire others.  When he announced that his cancer had returned in 2005, Arlen said, 'I have beaten a brain tumor, bypass heart surgery and many tough political opponents and I'm going to beat this, too,'" Obama wrote, adding that" Arlen fought that battle for seven more years with the same resolve he used to fight for stem-cell research funding, veterans health, and countless other issues that will continue to change lives for years to come."

The U.S. president conceded the release by saying: "Michelle and I send our thoughts and prayers to Joan and the rest of the Specter family."

Vice President Joe Biden also said in a statement: "For over three decades, I watched his political courage accomplish great feats and was awed by his physical courage to never give up.  Arlen never walked away from his principles and was at his best when they were challenged."

The Israeli embassy in the U.S. also responded to Specter's passing.
"The people of Israel deeply mourn the passing of Senator Arlen Specter, an unswerving defender of the Jewish State and a stalwart advocate of peace. He was a friend in the truest sense, and his dedication to Israel will never be forgotten. May his memory be blessed forever," the embassy said in a statement. 

National Jewish Democratic Council issued a statement saying "Senator Specter has left behind a proud legacy of public service that will hopefully guide future generations of public servants, Jewish and non-Jewish alike."

Republican Jewish Council National Chairman David Flaum said, "Arlen Specter was a devoted public servant with a great passion for justice. He was a staunch supporter of Israel in the U.S. Senate and during his tenure led efforts to expand and enhance the U.S.-Israel relationship."

In another response to news of Specter's death, the pro-Israel lobby AIPAC wrote: 'Time and time again, Sen. Specter worked to ensure that America’s ally had the resources necessary to defend herself and protect U.S. interests in the Middle East."

"He was a good friend of our organization and a leading architect of the congressional bond between our country and Israel," the AIPAC statement added.

Committee to Free Jonathan Pollard also commented on the passing of the veteran lawmaker, saying "Senator Specter was among the first to join the call for Pollard's release, his support was especially significant because of respect expressed by President Obama toward Senator."