Arlen Specter, the longest-serving U.S. senator in Pennsylvania history and a frequent and proud thorn in the side of both political parties, died on Sunday at age 82 from complications of non-Hodgkin's lymphoma. In his 30 years in the Senate, from 1981 until 2010, Specter championed an ideologically unorthodox course, generally opposing gun control and supporting abortion rights, the death penalty, stem-cell research, congressional earmarks for health research in his home state, and affirmative action.

Specter first earned a national name for himself as an assistant counsel to the Warren Commission set up to investigate the 1963 assassination of President John F. Kennedy — he was the chief architect of the controversial "single-bullet theory," which underpins the Warren Commission's conclusion that JFK was killed by a single gunman. A Democrat, Specter switched parties after winning election in 1965 as Philadelphia district attorney on the Republican ticket — in an end-run around the city's Democratic Party bosses — and he stayed in the GOP until 2009, when he famously switched back, largely to avoid a primary defeat from conservative challenger Patrick Toomey. He lost the Democratic primary instead, ending his political career (and starting Specter's brief career in academia and, oddly, stand-up comedy).

"The essential contradiction for Specter was that he was an obvious political opportunist but saw himself as a principled man buffeted by a changing world," says Mackenzie Weinger at Politico.

Specter "occupied a space in the Senate that no longer fits the current political environment: Raging centrist," says Paul Kane at The Washington Post. He "spent his career finding ways to enrage both ends of the ideological spectrum, throwing his always sharp elbows at liberals one month only to do the same to conservatives the next month." His hard-hitting, prosecutorial demeanor earned him the nickname "Snarlin' Arlen."

Although "Specter wielded an influential swing vote in the Senate," says Timothy Phelps at the Los Angeles Times, "he particularly distinguished himself, for better or worse, during his 14 Supreme Court confirmation hearings, when he habitually asked probing questions of nominees from both parties." Most famously, he is credited with sinking the nomination of conservative Judge Robert Bork in 1987, then saving the nomination of Supreme Court Justice Clarence Thomas by eviscerating Anita Hill, who alleged that Thomas had sexually harassed her, accusing Hill of "flat-out perjury."

Arlen Specter was born in 1930 in Wichita, Kansas, the youngest of four children of a Ukrainian immigrant father. He grew up in the only Jewish family in Bob Dole's hometown of Russell, Kan., peddling melons with his father then working in his junkyard. His family later moved to Philadelphia, Specter said, "so my sister could meet and marry a nice Jewish boy," and he graduated from the University of Pennsylvania in 1951. After serving two years in the Air Force, Specter earned a law degree from Yale in 1956. By 1959, he was an assistant DA in Philadelphia.

Specter is survived by his wife of 59 years, two sons, a sister, and four grandchildren. Vice President Joe Biden, who counted Specter among his close friends, will attend the funeral on behalf of the White House.

Here, quotes about Specter throughout his career:

"Arlen Specter was always a fighter. 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."
President Obama, Oct. 14

"He gave a lot of dedicated service to the country... I didn't always agree with him, but I was always amazed by his determination to be in the fight, to be in the debate, to look for a position that made him a significant factor in whatever discussion was going on."
Sen. Roy Blunt (R-Mo.), Oct. 14

"No member of Congress shaped the Supreme Court more than he did. He had a prosecutorial mindset. He could be incredibly persuasive as an interrogator."
G. Terry Madonna, public policy professor at Franklin & Marshall College, Oct. 14

"If you were involved in litigation you'd pick the toughest, smartest lawyer to litigate your case in front of a jury and that's Arlen Specter. He's the toughest, smartest guy in the room."
Former Specter chief of staff David Urban, Oct. 14

"Specter's greatest talent may be his unique ability to put himself — somehow, some way — in the center of the nation's most important debates. It's not just Specter's ubiquity, though, that has led us to think of him as an institution. It's also the niche he's carved out for himself as one of the few true wild cards of Washington politics. He is reviled by those on both the Right and the Left. Charming and churlish, brilliant and pedantic, he can be fiercely independent, entertainingly eccentric, and simply maddening."
Andrew Putz, Philadelphia Magazine, November 2006

"Arlen Specter is a jerk, but he's our jerk." 
Conservative activist Paul Weyrich in 1992, quoted in National Review

"Remember Popeye, who used to say, 'I am what I am'? I don't think anyone could dress me in different attire. I am what I am."
Arlen Specter, May 2010, right before losing the Democratic primary

Sources: CNN, The Los Angeles Times, The New York Times, Philadelphia Magazine, Politico, TIME, The Washington Post (2,3)