Ted Kennedy was the second-longest-serving member of the Senate, after Robert Byrd, of West Virginia, and the third-longest-serving member, ever.
He was "the youngest of nine and he was the youngest by four years," points out Peter Canellos, editor of "Last Lion: The Fall and Rise of Ted Kennedy."
"It was a pretty hard-driving (situation)," Canellos continued, "and very, very competitive. And so, he was spared some of the sort of relentlessness of his parents' expectations of the older kids."
Tragedy struck the Kennedys in 1946, when Joe Jr., a World War II Navy pilot, was killed in action. Ted's older brother, John (Jack), took on the role of eldest son.
"Jack was sort of serious and scholarly, and would try to teach Ted lessons," Canellos told CBS News.
Robert (Bobby) and Ted Kennedy helped Jack with his presidential campaign, then went on to become successful politicians themselves, each with his own style.
"Jack Kennedy was an intellectual and Teddy idolized him," Canellos says. "Bobby Kennedy was a hard-driven, sort of relentless striver in a lot of ways, and Ted was not. Ted was gregarious and friendly."
Tragedy struck the family again in 1963, when President John F. Kennedy was assassinated in Dallas.
"Ted took Jack's death very hard," notes Adam Clymer, author of "Edward M. Kennedy: A Biography."
"He was presiding in the Senate when the news came," Clymer told CBS News, "and he just fled the place. He grieved over it deeply, and worried, when Bob was thinking for running for president, worried that he might get shot."
Ted's fears came true. Just five years after Jack's death, presidential candidate Robert Kennedy was gunned down in Los Angeles.
"When Robert was killed," Clymer says, "he wasn't dead for an hour before people started walking up to Ted and telling him he ought to run for president, and he was utterly shaken by it."
"I think," says Canellos, "in 1968, when Bobby Kennedy was assassinated, (Ted) realized that the rest of his life wouldn't be spent on his own terms; it would be spent trying to live up to the legacy of two martyred brothers."
"A day doesn't go by," Ted once said, "when I'm not thoughtful about them, and I don't miss them in a very, very real way."
Over the course of nearly 47 years in the Senate, Ted Kennedy defined himself on his own terms and created his own legacy.
"I think he was the greatest senator of the 20th and, thus far, the 21st century," Clymer asserts. "I think that they would have indeed have been proud of him."
"It's clearly an end of an era," Canellos observed. "The Kennedy story has been one of the great narratives in American life and, through Ted Kennedy, it has extended for more than half-a-century. But that hope, that dream of the 60s of the New Frontier, dies with Ted Kennedy."