Senator Edward M. Kennedy of Massachusetts, a son of one of the most storied families in American politics, a man who knew triumph and tragedy in near-equal measure and who will be remembered as one of the most effective lawmakers in the history of the Senate, died Tuesday night. He was 77 .

The death was announced Wednesday morning in a statement by the Kennedy family.

“Edward M. Kennedy – the husband, father, grandfather, brother and uncle we loved so deeply – died late Tuesday night at home in Hyannis Port,” the statement said. “We’ve lost the irreplaceable center of our family and joyous light in our lives, but the inspiration of his faith, optimism, and perseverance will live on in our hearts forever. We thank everyone who gave him care and support over this last year, and everyone who stood with him for so many years in his tireless march for progress toward justice, fairness and opportunity for all. He loved this country and devoted his life to serving it. He always believed that our best days were still ahead, but it’s hard to imagine any of them without him.”

Mr. Kennedy had been in precarious health since he suffered a seizure in May 2008 at his home in Hyannis Port, Mass. His doctors determined the cause had been a malignant glioma, a brain tumor that often carries a grim prognosis.

As he underwent cancer treatment, Mr. Kennedy was little seen in Washington, appearing most recently at the White House in April as Mr. Obama signed a national service bill that bears the Kennedy name.

While he had been physically absent from the capital, his presence had been deeply felt as Congress weighed the most sweeping revisions to America’s health care system in decades, an effort Mr. Kennedy called “the cause of my life.”

On July 15, the Senate Health, Education, Labor and Pensions committee, which Mr. Kennedy heads, passed health care legislation that he had helped write and that may one day be regarded as the capstone to Mr. Kennedy’s government career.

Mr. Kennedy was the last surviving brother of a generation of Kennedys that dominated American politics in the 1960s and that came to embody glamour, political idealism and untimely death. The Kennedy mystique — some call it the Kennedy myth — has held the imagination of the world for decades and came to rest on the sometimes too-narrow shoulders of the brother known as Teddy.

Mr. Kennedy, who served 46 years as the most well-known Democrat in the Senate, longer than all but two other senators, was the only one of those brothers to die after reaching old age. President John F. Kennedy and Senator Robert F. Kennedy were felled by assassins’ bullets in their 40s. The eldest brother, Joseph P. Kennedy Jr., died in 1944 at the age of 29 while on a risky World War II bombing mission.

Mr. Kennedy spent much of last year in treatment and recuperation, broken by occasional public appearances and a dramatic return to the Capitol last summer to cast a decisive vote on a Medicare bill.

He electrified the opening night of the Democratic National Convention in Denver in August with an unscheduled appearance and a speech that had delegates on their feet. Many were in tears.

His gait was halting, but his voice was strong. “My fellow Democrats, my fellow Americans, it is so wonderful to be here, and nothing is going to keep me away from this special gathering tonight,” Mr. Kennedy said. “I have come here tonight to stand with you to change America, to restore its future, to rise to our best ideals and to elect Barack Obama president of the United States.”

Senator Kennedy was at or near the center of much of American history in the latter part of the 20th century and the early years of the 21st. For much of his adult life, he veered from victory to catastrophe, winning every Senate election he entered but failing in his only try for the presidency; living through the sudden deaths of his brothers and three of his nephews; being responsible for the drowning death on Chappaquiddick Island of a young woman, Mary Jo Kopechne, a former aide to his brother Robert. One of the nephews, John F. Kennedy Jr., who the family hoped would one day seek political office and keep the Kennedy tradition alive, died in a plane crash in 1999 at age 38.

Mr. Kennedy himself was almost killed, in 1964, in a plane crash, which left him with permanent back and neck problems.

He was a Rabelaisian figure in the Senate and in life, instantly recognizable by his shock of white hair, his florid, oversize face, his booming Boston brogue, his powerful but pained stride. He was a celebrity, sometimes a self-parody, a hearty friend, an implacable foe, a man of large faith and large flaws, a melancholy character who persevered, drank deeply and sang loudly. He was a Kennedy.

Senator Robert C. Byrd, Democrat of West Virginia, one of the institution’s most devoted students, said of his longtime colleague, “Ted Kennedy would have been a leader, an outstanding senator, at any period in the nation’s history.”

Mr. Byrd is one of only two senators to have served longer in the chamber than Mr. Kennedy; the other was Strom Thurmond of South Carolina. In May 2008, on learning of Mr. Kennedy’s diagnosis of a lethal brain tumor, Mr. Byrd wept openly on the floor of the Senate.

Born to one of the wealthiest American families, Mr. Kennedy spoke for the downtrodden in his public life while living the heedless private life of a playboy and a rake for many of his years. Dismissed early in his career as a lightweight and an unworthy successor to his revered brothers, he grew in stature over time by sheer longevity and by hewing to liberal principles while often crossing the partisan aisle to enact legislation. A man of unbridled appetites at times, he nevertheless brought a discipline to his public work that resulted in an impressive catalog of legislative achievement across a broad landscape of social policy.

Mr. Kennedy left his mark on legislation concerning civil rights, health care, education, voting rights and labor. He was chairman of the Senate Committee on Health, Education, Labor and Pensions at his death. But he was more than a legislator. He was a living legend whose presence insured a crowd and whose hovering figure haunted many a president.

Although he was a leading spokesman for liberal issues and a favorite target of conservative fund-raising appeals, the hallmark of his legislative success was his ability to find Republican allies to get bills passed. Perhaps the last notable example was his work with President George W. Bush to pass the No Child Left Behind education law pushed by Mr. Bush in 2001. He also co-sponsored immigration legislation with Senator John McCain, the 2008 Republican presidential nominee. One of his greatest friends and collaborators in the Senate was Orrin Hatch, the Utah Republican.

Mr. Kennedy had less impact on foreign policy than on domestic concerns, but when he spoke his voice was influential. He led the Congressional effort to impose sanctions on South Africa over apartheid, pushed for peace in Northern Ireland, won a ban on arms sales to the dictatorship in Chile and denounced the Vietnam War. In 2002, he voted against authorizing the Iraq war; later, he called that opposition “the best vote I’ve made in my 44 years in the United States Senate.”

At a pivotal moment in the 2008 Democratic presidential primaries, Mr. Kennedy endorsed Senator Obama for president, saying Mr. Obama offered America a chance for racial reconciliation and an opportunity to turn the page on the polarizing politics of the past several decades.

“He will be a president who refuses to be trapped in the patterns of the past,” Mr. Kennedy told an Obama rally in Washington on Jan. 28, 2008. “He is a leader who sees the world clearly, without being cynical. He is a fighter who cares passionately about the causes he believes in without demonizing those who hold a different view.”

Mr. Kennedy struggled for much of his life with his weight, with alcohol and with persistent tales of womanizing. In an Easter break episode in 1991 in Palm Beach, Fla., he went out drinking with his son Patrick and a nephew, William Kennedy Smith, on the night that Mr. Smith was accused of raping a woman. Mr. Smith was prosecuted in a lurid trial that fall but was acquitted.

Mr. Kennedy’s personal life stabilized in 1992 with his marriage to Victoria Anne Reggie, a Washington lawyer. His first marriage, to Joan Bennett Kennedy, ended in divorce in 1982 after 24 years.

Senator Kennedy served as a surrogate father to his brothers’ children and worked to keep the Kennedy flame alive through the Kennedy Library in Boston, the Kennedy Center in Washington and the Kennedy School of Government at Harvard University, where he helped establish the Institute of Politics.

In December, Harvard granted Mr. Kennedy a special honorary degree. He referred to Mr. Obama’s election as “not just a culmination, but a new beginning.”

He then spoke of his own life, and perhaps his legacy.

“We know the future will outlast all of us, but I believe that all of us will live on in the future we make,” he said. “I have lived a blessed time.”

Kennedy family courtiers and many other Democrats believed he would eventually win the White House and redeem the promise of his older brothers. In 1980, he took on the president of his own party, Jimmy Carter, but fell short because of Chappaquiddick, a divided party and his own weaknesses as a candidate, including an inability to articulate why he sought the office.

But as that race ended in August at the Democratic National Convention in New York, Mr. Kennedy delivered his most memorable words, wrapping his dedication to party principles in the gauzy cloak of Camelot.

“For me, a few hours ago, this campaign came to an end,” Mr. Kennedy said in the coda to a speech before a rapt audience at Madison Square Garden and on television. “For all those whose cares have been our concern, the work goes on, the cause endures, the hope still lives, and the dream shall never die.”

A Family Steeped in Politics

Born Feb. 22, 1932, in Brookline, Mass., just outside Boston, Edward Moore Kennedy grew up in a family of shrewd politicians. Both his father, Joseph P. Kennedy, and his mother, the former Rose Fitzgerald, came from prominent Irish-Catholic families with long involvement in the hurly-burly of Democratic politics in Boston and Massachusetts. His father, who made a fortune in real estate, movies and banking, served in President Franklin D. Roosevelt’s administration, as the first chairman of the Securities and Exchange Commission and then as ambassador to Britain.

There were nine Kennedy children, four boys and five girls, with Edward the youngest. They grew up talking politics, power and influence because those were the things that preoccupied the mind of Joseph Kennedy. As Rose Kennedy, who took responsibility for the children’s Roman Catholic upbringing, once put it: “My babies were rocked to political lullabies.”

When Edward was born, President Herbert Hoover sent Rose a bouquet of flowers and a note of congratulations. The note came with 5 cents postage due; the framed envelope is a family heirloom.

It was understood among the children that Joseph P. Kennedy Jr., the oldest boy, would someday run for Congress and, his father hoped, the White House. When Joseph Jr. was killed in World War II, it fell to the next oldest son, John F., to run. As John said at one point in 1959 while serving in the Senate: “Just as I went into politics because Joe died, if anything happened to me tomorrow, Bobby would run for my seat in the Senate. And if Bobby died, our young brother, Ted, would take over for him.”

Although surrounded by the trappings of wealth — stately houses, servants and expensive cars — young Teddy did not enjoy a settled childhood. He bounced among the family homes in Boston, New York, London and Palm Beach, and by the time Edward was ready to enter college, he had attended 10 preparatory schools in the United States and England, finally finishing at Milton Academy, near Boston. He said that the constant moving had forced him to become more genial with strangers; indeed, he grew to be more of a natural politician than either John or Robert.

After graduating from Milton in 1950, where he showed a penchant for debating and sports but was otherwise an undistinguished student, Mr. Kennedy enrolled in Harvard, as had his father and brothers. It was at Harvard, in his freshman year, that he ran into the first of several personal troubles that were to dog him for the rest of his life: He persuaded another student to take his Spanish examination, got caught and was forced to leave the university.

Suddenly draft-eligible during the Korean War, Mr. Kennedy enlisted in the Army and served two years, securing, with his father’s help, a cushy post at NATO headquarters in Paris. In 1953, he was discharged with the rank of private first class.

Re-enrolling in Harvard, he became a more serious student, majoring in government, excelling in public speaking and playing first-string end on the football team. He graduated in 1956 with a Bachelor of Arts degree, then enrolled in the University of Virginia School of Law, where Robert had studied. There, he won the moot court competition and took a degree in 1959. Later that year, he was admitted to the Massachusetts bar.

Mr. Kennedy’s first foray into politics came in 1958, while still a law student, when he managed John’s Senate re-election campaign. There was never any real doubt that Massachusetts voters would return John Kennedy to Washington, but it was a useful internship for his youngest brother.

That same year, Mr. Kennedy married Virginia Joan Bennett, a debutante from Bronxville, a New York suburb where the Kennedys had once lived. In 1960, when John Kennedy ran for president, Edward was assigned a relatively minor role, rustling up votes in Western states that usually voted Republican. He was so enthusiastic about his task that he rode a bronco at a Montana rodeo and daringly took a ski jump at a winter sports tournament in Wisconsin to impress a crowd. The episodes were evidence of a reckless streak that repeatedly threatened his life and career.

John Kennedy’s election to the White House left vacant a Senate seat that the family considered its property. Robert Kennedy was next in line, but chose the post of attorney general instead (an act of nepotism that has since been outlawed). Edward was only 28, two years shy of the minimum age for Senate service.

So the Kennedys installed Benjamin A. Smith 2d, a family friend, as a seat-warmer until 1962, when a special election would be held and Edward would have turned 30. Edward used the time to travel the world and work as an assistant district attorney in Boston, waiving the $5,000 salary and serving instead for $1 a year.

As James Sterling Young, the director of a Kennedy Oral History Project at the University of Virginia, put it: “Most people grow up and go into politics. The Kennedys go into politics and then they grow up.”

Less than a month after turning 30 in 1962, Mr. Kennedy declared his candidacy for the remaining two years of his brother’s Senate term. He entered the race with a tailwind of family money and political prominence. Nevertheless, Edward J. McCormack Jr., the state’s attorney general and a nephew of John W. McCormack, then speaker of the United States House of Representatives, also decided to go after the seat.

It was a bitter fight, with a public rehash of the Harvard cheating episode and with Mr. McCormack charging in a televised “Teddy-Eddie” debate that Mr. Kennedy lacked maturity of judgment because he had “never worked for a living” and had never held elective office. “If your name was simply Edward Moore instead of Edward Moore Kennedy,” Mr. McCormack added, “your candidacy would be a joke.”

But the Kennedys had ushered in an era of celebrity politics, which trumped qualifications in this case. Mr. Kennedy won the primary by a two-to-one ratio, then went on to easy victory in November against the Republican candidate, George Cabot Lodge, a member of an old-line Boston family that had clashed politically with the Kennedys through the years.

When Mr. Kennedy entered the Senate in 1962, he was aware that he might be seen as an upstart, with one brother in the White House and another in the cabinet. He sought guidance on the very first day from one of the Senate’s most respected elders, Richard Russell of Georgia. “You go further if you go slow,” Senator Russell advised.

Mr. Kennedy took things slowly, especially that first year. He did his homework, was seen more than he was heard and was deferential to veteran legislators.

On Friday, Nov. 22, 1963, he was presiding over the Senate when a wire service ticker in the lobby brought the news of John Kennedy’s shooting in Dallas. Violence had claimed the second of Joseph Kennedy’s sons.

Edward was sent to Hyannis Port to break the news to his father, who had been disabled by a stroke. He returned to Washington for the televised funeral and burial, the first many Americans had seen of him. He and Robert had planned to read excerpts from John’s speeches at the Arlington burial service. At the last moment they chose not to.

A friend described him as “shattered — calm but shattered.”

A Deadly Plane Crash

Robert moved into the breach and was immediately discussed as a presidential prospect. Edward became a more prominent family spokesman.

The next year, he was up for re-election. A heavy favorite from the start, he was on his way to the state convention that was to renominate him when his light plane crashed in a storm near Westfield, Mass. The pilot and a Kennedy aide were killed, and Mr. Kennedy’s back and several ribs were broken. Senator Birch Bayh of Indiana pulled Mr. Kennedy from the plane.

The senator was hospitalized for the next six months, suspended immobile between a frame that resembled a waffle iron. His wife, Joan, carried on his campaign, mainly by advising voters that he was steadily recovering. He won easily over a little-known Republican, Howard Whitmore Jr.

During his convalescence, Mr. Kennedy devoted himself to his legislative work. He was briefed by a parade of Harvard professors and began to develop his positions on immigration, health care and civil rights.

“I never thought the time was lost,” he said later. “I had a lot of hours to think about what was important and what was not and about what I wanted to do with my life.”

He returned to the Senate in 1965, joining his brother Robert, who had won a seat from New York. Edward promptly entered a major fight, his first. President Lyndon B. Johnson’s Voting Rights Act was up for consideration, and Mr. Kennedy tried to strengthen it with an amendment that would have outlawed poll taxes. He lost by only four votes, serving lasting notice on his colleagues that he was a rapidly maturing legislator who could prepare a good case and argue it effectively.

Mr. Kennedy was slow to oppose the war in Vietnam, but in 1968, shortly after Robert decided to seek the presidency on an antiwar platform, Edward called the war a “monstrous outrage.”

Robert Kennedy was shot on June 5, 1968, as he celebrated his victory in the California primary, becoming the third of Joseph Kennedy’s sons to die a violent death. Edward was in San Francisco at a victory celebration. He commandeered an Air Force plane and flew to Los Angeles.

Frank Mankiewicz, Robert’s press secretary, saw Edward “leaning over the sink with the most awful expression on his face.”

“Much more than agony, more than anguish — I don’t know if there’s a word for it,” Mr. Mankiewicz said, recalling the encounter in “Edward M. Kennedy: A Biography,” by Adam Clymer (William Morrow, 1999).

Robert’s death draped Edward in the Kennedy mantle long before he was ready for it and forced him to confront his own mortality. But he summoned himself to deliver an eloquent eulogy at St. Patrick’s Cathedral in New York.

“My brother need not be idealized, or enlarged in death beyond what he was in life, to be remembered simply as a good and decent man, who saw wrong and tried to right it, saw suffering and tried to heal it, saw war and tried to stop it,” Mr. Kennedy said, his voice faltering. “Those of us who loved him and who take him to his rest today pray that what he was to us and what he wished for others will someday come to pass for all the world.”

A New Role as Patriarch

After the funeral, Edward Kennedy withdrew from public life and spent several months brooding, much of it while sailing off the New England coast.

Near the end of the summer of 1968, he emerged from seclusion, the sole survivor of Joseph Kennedy’s boys, ready to take over as family patriarch and substitute father to John’s and Robert’s 13 children, seemingly eager to get on with what he called his “public responsibilities.”

“There is no safety in hiding,” he declared in a speech at Holy Cross College in Worcester, Mass., in August. “Like my brothers before me, I pick up a fallen standard. Sustained by the memory of our priceless years together, I shall try to carry forward that special commitment to justice, excellence and courage that distinguished their lives.”

There was some talk of his running for president at that point. But he ultimately endorsed Hubert H. Humphrey in his losing campaign to Richard M. Nixon.

Mr. Kennedy focused more on bringing the war in Vietnam to an end and on building his Senate career. Although only 36, he challenged Senator Russell B. Long of Louisiana, one of the shrewdest, most powerful legislators on Capitol Hill, for the post of deputy majority leader. Fellow liberals sided with him, and he edged Mr. Long by five votes to become the youngest assistant majority leader, or whip, in Senate history.

He plunged into the new job with Kennedy enthusiasm. But fate, and the Kennedy recklessness, intervened on July 18, 1969. Mr. Kennedy had been at a party with several women who had been aides to Robert. The party, a liquor-soaked barbecue, was held at a rented cottage on Chappaquiddick Island, off Martha’s Vineyard. He left around midnight with Mary Jo Kopechne, 28, took a turn away from the ferry landing and drove the car off a narrow bridge on an isolated beach road. The car sank in eight feet of water, but he managed to escape. Miss Kopechne, a former campaign worker for Robert, drowned.

Mr. Kennedy did not report the accident to the authorities for almost 10 hours, explaining later that he had been so banged about by the crash that he had suffered a concussion, and that he had become so exhausted while trying to rescue Miss Kopechne that he had gone immediately to bed. A week later, he pleaded guilty to a charge of leaving the scene of an accident and was given a two-month suspended sentence.

But that was far from the end of the incident. Questions lingered in the minds of the Massachusetts authorities and of the general public. Why was the car on an isolated road? Had he been drinking? (Mr. Kennedy testified at an inquest that he had had two drinks.) What sort of relationship did Mr. Kennedy and Miss Kopechne have? Could she have been saved if he had sought help immediately? Why did the senator tell his political advisers about the accident before reporting it to the police?

The controversy became so intense that Mr. Kennedy went on television to ask Massachusetts voters whether he should resign from office. He conceded that his actions after the crash had been “indefensible.” But he steadfastly denied any intentional wrongdoing.

His constituents sent word that he should remain in the Senate. And little more than a year later, he easily won re-election to a second full term, again defeating a little-known Republican, Josiah A. Spaulding, by a three-to-two ratio. But his heart did not seem to be in his work any longer. He was sometimes absent from Senate sessions and neglected his whip duties. Senator Byrd, of West Virginia, took the job away from him by putting together a coalition of Southern and border-state Democrats to vote him out.

That loss shook Mr. Kennedy out of his lethargy. He rededicated himself to his role as a legislator. “It hurts like hell to lose,” he said, “but now I can get around the country more. And it frees me to spend more time on issues I’m interested in.” Many years later, he became friends with Mr. Byrd and told him the defeat had been the best thing that could have happened in his Senate career.

Turmoil at Home

In the next decade, Mr. Kennedy expanded on his national reputation, first pushing to end the war in Vietnam, then concentrating on his favorite legislative issues, especially civil rights, health, taxes, criminal laws and deregulation of the airline and trucking industries. He traveled the country, making speeches that kept him in the public eye.

But when he was mentioned as a possible candidate for president in 1972, he demurred; and when the Democratic nominee, George S. McGovern, offered him the vice-presidential nomination, Mr. Kennedy again said no, not wanting to face the inevitable Chappaquiddick questions.

In 1973, his son Edward M. Kennedy Jr., then 12, developed a bone cancer that cost him a leg. The next year, Mr. Kennedy took himself out of the 1976 race. Instead, Mr. Kennedy easily won a third full term in the Senate, and Jimmy Carter, a former one-term governor of Georgia, moved into the White House.

In early 1978, Mr. Kennedy’s wife, Joan, moved out of their sprawling contemporary house overlooking the Potomac River near McLean, Va., a Washington suburb. She took up residence in an apartment of her own in Boston, saying she wanted to “explore options other than being a housewife and mother.” But she also acknowledged a problem with alcohol, and conceded that she was increasingly uncomfortable with the pressure-cooker life that went with membership in the Kennedy clan. She began studying music and enrolled in a program for alcoholics.

The separation posed not only personal but also political problems for the senator. After Mrs. Kennedy left for Boston, there were rumors that linked the senator with other women. He maintained that he still loved his wife and indicated that the main reason for the separation was Mrs. Kennedy’s desire to work out her alcohol problem. She subsequently campaigned for him in the 1980 race, but there was never any real reconciliation, and they eventually entered divorce proceedings.

Although Mr. Kennedy supported Mr. Carter in 1976, by late 1978 he was disenchanted. Polls indicated that the senator was becoming popular while the president was losing support. In December, at a midterm Democratic convention in Memphis, Mr. Kennedy could hold back no longer. He gave a thundering speech that, in retrospect, was the opening shot in the 1980 campaign.

“Sometimes a party must sail against the wind,” he declared, referring to Mr. Carter’s economic belt-tightening and political caution. “We cannot heed the call of those who say it is time to furl the sail. The party that tore itself apart over Vietnam in the 1960s cannot afford to tear itself apart today over budget cuts in basic social programs.”

Mr. Kennedy did not then declare his candidacy. But draft-Kennedy groups began to form in early 1979, and some Democrats up for re-election in 1980 began to cast about for coattails that were longer than Mr. Carter’s.

After consulting advisers and family members over the summer of 1979, Mr. Kennedy began speaking openly of challenging the president, and on Nov. 7, 1979, he announced officially that he would run. “Our leaders have resigned themselves to defeat,” he said.

The campaign was a disaster, badly organized and appearing to lack a political or policy premise. His speeches were clumsy, and his delivery was frequently stumbling and bombastic. And in the background, Chappaquiddick always loomed. He won the New York and California primaries, but the victories were too little and came too late to unseat Mr. Carter. At the party’s nominating convention in New York, however, he stole the show with his “dream shall never die” speech.

With the approach of the 1984 election, there was the inevitable speculation that Mr. Kennedy, who had easily won re-election to the Senate in 1982, would again seek the presidency. He prepared and planned a campaign. But in the end he chose not to run, saying he wanted to spare his family a repeat of the ordeal they went through in 1980. Skeptics said he also knew he could not fight the undertow of Chappaquiddick.

A Full-On Senate Focus

Freed at last of the expectation that he should and would seek the White House, Mr. Kennedy devoted himself fully to his day job in the Senate. He led the fight for the 18-year-old vote, the abolition of the draft, deregulation of the airline and trucking industries, and the post-Watergate campaign finance legislation. He was deeply involved in renewals of the Voting Rights Act and the Fair Housing law of 1968. He helped establish the Occupational Safety and Health Administration. He built federal support for community health care centers, increased cancer research financing and helped create the Meals on Wheels program. He was a major proponent of a health and nutrition program for pregnant women and infants.

When Republicans took over the Senate in 1981, Mr. Kennedy requested the ranking minority position on the Labor and Public Welfare Committee, asserting that the issues before the labor and welfare panel would be more important during the Reagan years.

In the years after his failed White House bid, Mr. Kennedy also established himself as someone who made “lawmaker” mean more than a word used in headlines to describe any member of Congress. Though his personal life was a mess until his remarriage in the early 1990s, he never failed to show up prepared for a committee hearing or a floor debate.

His most notable focus was civil rights, “still the unfinished business of America,” he often said. In 1982, he led a successful fight to defeat the Reagan administration’s effort to weaken the Voting Rights Act.

In one of those bipartisan alliances that were hallmarks of his legislative successes, Mr. Kennedy worked with Senator Bob Dole, Republican of Kansas, to secure passage of the voting rights measure, and Mr. Dole got most of the credit.

Perhaps his greatest success on civil rights came in 1990 with passage of the Americans with Disabilities Act, which required employers and public facilities to make “reasonable accommodation” for the disabled. When the law was finally passed, Mr. Kennedy and others told how their views on the bill had been shaped by having relatives with disabilities. Mr. Kennedy cited his mentally disabled sister, Rosemary, and his son who had lost a leg to cancer.

Mr. Kennedy was one of Bill and Hillary Clinton’s strongest allies in their failed 1994 effort to enact national health insurance, a measure the senator had been pushing, in one form or another, since 1969.

But he kept pushing incremental reforms, and in 1997, teaming with Senator Hatch, Mr. Kennedy helped enact a landmark health care program for children in low-income families, a program now known as the State Children’s Health Insurance Program, or S-Chip.

He led efforts to increase aid for higher education and win passage of Mr. Bush’s No Child Left Behind Act. He pushed for increases in the federal minimum wage. He helped win enactment of the Medicare prescription drug benefit, one of the largest expansions of government health aid ever.

He was a forceful and successful opponent of the confirmation of Robert H. Bork to the Supreme Court. In a speech delivered within minutes of President Reagan’s nomination of Mr. Bork in 1987, Mr. Kennedy made an attack that even friendly commentators called demagogic. Mr. Bork’s “extremist view of the Constitution,” he said, meant that “Robert Bork’s America is a land in which women would be forced into back-alley abortions, blacks would sit at segregated lunch counters, rogue police could break down citizens’ doors in midnight raids, and schoolchildren could not be taught about evolution, writers and artists could be censored at the whim of government, and the doors of the federal courts would be shut on the fingers of millions of Americans.”

Some of Mr. Kennedy’s success as a legislator can be traced to the quality and loyalty of his staff, considered by his colleagues and outsiders alike to be the best on Capitol Hill.

“He has one of the most distinguished alumni associations of any U.S. senator,” said Ross K. Baker, a political scientist at Rutgers University who has worked in Congress. “To have served in even a minor capacity in the Kennedy office or on one of his committees is a major entry in anyone’s résumé.”

Those who have worked for Mr. Kennedy include Stephen G. Breyer, appointed to the Supreme Court by President Clinton; Gregory B. Craig, now the White House counsel; and Kenneth R. Feinberg, the Obama administration’s top official for compensation.

Mr. Kennedy “deserves recognition not just as the leading senator of his time, but as one of the greats in its history, wise in the workings of this singular institution, especially its demand to be more than partisan to accomplish much,” Mr. Clymer wrote in his biography.

“The deaths and tragedies around him would have led others to withdraw. He never quits, but sails against the wind.”

Mr. Kennedy is survived by his wife, known as Vicki; two sons, Edward M. Kennedy Jr. of Branford, Conn., and United States Representative Patrick J. Kennedy of Rhode Island; a daughter, Kara Kennedy Allen, of Bethesda, Md.; two stepchildren, Curran Raclin and Caroline Raclin, and four grandchildren. His former wife, Joan Kennedy, lives in Boston.

Mr. Kennedy is also survived by a sister, Jean Kennedy Smith, of New York. On Tuesday, his sister Eunice Kennedy Shriver of Potomac, Md., died at age 88. Another sister, Patricia Lawford Kennedy, died in 2006. His sister Rosemary died in 2005, and his sister Kathleen died in a plane crash in 1948.

Their little brother Teddy was the youngest, the little bear whom everyone cuddled, whom no one took seriously and from whom little was expected. He reluctantly and at times awkwardly carried the Kennedy standard, with all it implied and all it required. And yet, some scholars contend, he may have proved himself the most worthy.

“He was a quintessential Kennedy, in the sense that he had all the warts as well as all the charisma and a lot of the strengths,” said Norman J. Ornstein, a political scientist at the American Enterprise Institute. “If his father, Joe, had surveyed, from an early age up to the time of his death, all of his children, his sons in particular, and asked to rank them on talents, effectiveness, likelihood to have an impact on the world, Ted would have been a very poor fourth. Joe, John, Bobby ... Ted.

“He was the survivor,” Mr. Ornstein continued. “He was not a shining star that burned brightly and faded away. He had a long, steady glow. When you survey the impact of the Kennedys on American life and politics and policy, he will end up by far being the most significant.”