At 74, Edward Kennedy still roars as one of America's leading liberal voices, longest serving US senators and most polarising political figures. While most people his age are retired, Kennedy shrugs off an achy back and heads toward anticipated re-election in November to an eighth six-year term.
"There's a lot to do," he said in a recent interview when asked to explain what even critics describe as his seemingly tireless efforts on behalf of the downtrodden.
"I think most of all it's the injustice that I continue to see and the opportunity to have some impact on it," the white-haired Massachusetts Democrat said.
Kennedy is now helping lead a drive to revamp US immigration laws while he keeps speaking out on such trademark issues as civil rights, education and health care.
Time magazine recently named Kennedy as one of "America's 10 best senators," calling him "the dealmaker." The recognition comes nearly 37 years after the Chappaquiddick scandal that tarnished his reputation and prospects of becoming president.
At rallies, congressional hearings and in the Senate, Kennedy orates with a booming voice. Sometimes it has the cadence of a drum roll, other times the fury of fireworks.
In his office this day, he talks softly and slowly.
"The defining aspect of our country is opportunity -- the hope that you can do better, that your children can do better," Kennedy said. "But you need an even playing field."
"To do that, you can't be sick and be in school. You've got to have health care. You've got to have an economy working to give people a chance to get ahead. It is not guaranteed. But you have to have an opportunity."
"Our country is big enough and strong enough and wealthy enough to give that kind of opportunity to everybody. That's what I work on every day," he said.
Kennedy came to the Senate in November 1962 to fill a seat earlier held by his older brother, then President John Kennedy.
Initially seen as a lightweight, the younger Kennedy became a Senate workhorse.
He showed he could be a partisan Democrat. He has been a leading critic of Republican President George W. Bush, particularly on his Iraq war, tax cuts for the rich and conservative nominees to the US Supreme Court who he fears will push the high court to the right.
But he also showed he could find common ground with Republicans.
Over the years, Kennedy has helped enact legislation to protect civil rights, expand health care, upgrade schools, increase student aid and crack down on discrimination.
Along the way, Kennedy also became a favourite target of conservatives, who can raise campaign money by just mentioning his name which has long been synonymous with such hot-button liberal causes as abortion rights and gay rights.
"He can be a lightning rod for my side," said Senator John Cornyn, a Texas Republican who has crossed swords with Kennedy. Yet Cornyn speaks of Kennedy with admiration.
"He comes to play every day. He's always prepared and has the energy and courage of conviction to keep fighting the fight," Cornyn said.
"You don't see a lot of senators do that -- at least not at the level Kennedy does, day in and day out," said Cornyn, a first-term senator. "I'd like to earn that reputation."
Cornyn and Kennedy are now locked in a battle over immigration that has divided the Republican-led Congress.
Cornyn favours tough border control while Kennedy backs an approach that would mix stricter security with what critics denounce as amnesty.
It would give most of the estimated 11.5 million to 12 million illegal immigrants in the country a chance for citizenship -- provided they pay back taxes, work and clear such hurdles as showing a knowledge of English.
"Are you with us?" Kennedy roared at an April 10 rally in Washington that drew tens of thousands of immigrants and their supporters.
"Yes," the crowd replied.
"I'm for you and you and you and you," he shouted.
"Kennedy, Kennedy, Kennedy," they cried.
In an interview that day, Kennedy likened demonstrations by immigrants to the civil rights movement by black Americans four decades ago. He also talked about a letter he received when he was just 8 years old from his father Joseph Kennedy, then US ambassador to England during World War Two.
"'I hope you will dedicate your life to trying to solve problems and relieve misery,'" Kennedy quoted his father as urging him.
"It's always echoed in my mind," Kennedy said.
Kennedy often invokes the memory of two of his older brothers -- John, slain while president in 1963, and Robert, assassinated while running for president in 1968.
"I think about my brothers every day," Kennedy told Reuters. "They set high standards. Sometimes you measure up, sometimes you don't."
Kennedy was dogged by personal problems early in life, most notably a 1969 accident in Chappaquiddick, Massachusetts, that took the life of a young woman who drowned when his car plunged off a bridge after a night of partying.
Asked if he was haunted by past missteps that may have cost him the White House, Kennedy replied: "I've said that I've made mistakes and taken responsibility for those mistakes.
"I have tried to learn from my mistakes and sought to be better in the course of my life -- better husband, better brother, better father, better grandfather, better senator."
Kennedy will go down as in history as one of the most influential senators as well as one of the longest-serving. Only West Virginia's Robert Byrd and the late Strom Thurmond of South Carolina served longer, more than 47 years.
Now in his 43rd year, Kennedy does not say how long he will stay. With a laugh, he said, "I get asked that a lot by my nieces and nephews. I tell them, 'I'm going to stay until I get the hang of it.'"
Kennedy recently wrote his sixth book, "America Back On Track." In it, he writes that the nation is at a crossroads and offers proposals to bring it together and move it ahead.
On immigration, this Irish-American writes: "In the march of progress, immigrants deserve our commitment as well. In my family, we were vividly aware of the immigrant stories of our great-grandparents. All found the American dream, and I have been one of its fortunate beneficiaries."