"I've never seen as much undaunted courage as Arlen had - both physically and politically. He believed he could change the world, if he just worked hard enough at it," Vice President Joe Biden told mourners, including three Pennsylvania governors, federal judges and hundreds of friends, at Har Zion Temple in Narberth, a Philadelphia suburb.
Specter died at his suburban home on Sunday at 82 after battling non-Hodgkin lymphoma. He had spent 30 years in the Senate before losing his seat in 2010, after crossing party lines to vote for President Barack Obama's stimulus package and later switching parties.
"In a dark time for our nation, he was willing to lose his seat to cast a decisive vote," said Specter's son Shanin, whose remarks capped about 90 minutes of tributes.
U.S. District Judge Jan DuBois recalled how his friend approached everything in life "with intensity, determination and grit," managing to teach one last law class on Oct. 4 at the University of Pennsylvania, even as he was losing his third fight with cancer.
Specter's influence on law, medicine, politics, Judaism and other walks of life was clear from the diverse, bipartisan and powerful crowd of mourners, including Democratic U.S. Sen. Bob Casey, Republican Gov. Tom Corbett and rows dotted with current and former members of Congress, along with federal judges whose careers Specter backed.
Specter, a political moderate, switched parties twice but mostly served as a Republican. Speakers said he honed his respect for opposing viewpoints as a child, growing up in the only Jewish family in Russell, Kan.
"He really set the standard for working across party lines and we're going to miss that," said Casey, who said Specter had helped smooth his transition when he arrived in Washington.
Anthony J. Scirica, the chief judge on the 3rd U.S. Circuit Court of Appeals, called Specter "irreplaceable."
"He touched so many lives," Scirica said. "He had some tough times, but he always thought that he was working for the public good."
Two of Specter's granddaughters also spoke, including Silvi Specter, a freshman at Penn who drew applause when she said she hopes to follow her grandfather into law and the U.S. Senate - before becoming president.
Shanin Specter, a prominent Philadelphia lawyer, compared his father to the fictional character Forrest Gump, given Specter's proximity to so many seminal events in modern American history.
Specter served as counsel to the Warren Commission investigating President John F Kennedy's death. He won his Senate seat in the Reagan landslide of 1980 and, as one of the Senate's sharpest legal minds, took part in 14 Supreme Court confirmation hearings.
He grilled Anita Hill when the law professor raised sexual harassment complaints against then-Supreme Court nominee Anita Hill. That cost him some of the support he enjoyed from female voters, but, much like the stimulus vote, he felt it was the right thing to do, former Democratic Gov. Ed Rendell recalled.
All the while, Specter fought two earlier bouts with Hodgkin lymphoma, and overcame a brain tumor and cardiac arrest following bypass surgery.
His greatest legacy, his friends said, may be the $10 million in federal money he steered into cancer research.
"There are some things that even the most robust human spirit can't conquer," said Rendell, choking up.
Specter is also survived by his wife, Joan, son Steve and three other granddaughters.