(CNN) -- Sen. Edward "Teddy" Kennedy -- patriarch of the first family of U.S. Democratic politics -- now faces the battle of his life after doctors disclosed he is suffering from a malignant brain tumor.
"I think all we can do is offer our hopes and prayers for him and to hope that he pulls this out just like he's pulled out so many tough situations," said Peter Fenn, a Democratic strategist and longtime friend.
Kennedy, 76, has represented Massachusetts in the U.S. Senate since his election in 1962. He is one of only six senators in U.S. history to serve more than 40 years.
Though the White House eluded his grasp, Kennedy is considered one of the most effective legislators of the past few decades. Learn more about Kennedy »
He had major roles in passage of the Civil Rights Act of 1964, the Voting Rights Act of 1965, the 1990 Americans with Disabilities Act, the 1993 Family and Medical Leave Act, the Kennedy-Hatch Law of 1997 and two increases in the minimum wage.
He endorsed Barack Obama for president before Super Tuesday's primaries, support that was considered a boon for the candidate. Learn more about Kennedy's condition »
"Sen. Ted Kennedy's legacy in the United States Senate is comparable and consistent with the legacy of his entire family for generations," Kennedy's biographer, Ted Sorensen, said Tuesday.
He launched his political career in 1962, when he was elected to finish the unexpired Senate term of his brother, John F. Kennedy, who was elected president in 1960 -- the seat had been held for two years by another person, who stepped aside in 1962.
Edward Kennedy was re-elected in 1964. That same year, he broke his back in a plane crash that killed an aide.
He has been elected to eight full terms, and is now the second most senior member of the Senate. Watch CNN's Bill Schneider assess Kennedy's sway over the Democratic Party »
During his career, he has championed social causes such as health care, education, family leave and the minimum wage. He is the author of "In Critical Condition: The Crisis in America's Health Care."
Kennedy chairs the Health, Education, Labor and Pensions Committee, and is a ranking member of the Judiciary and Armed Services committees.
Like his brothers, John and Robert, Edward Kennedy attended Harvard. He studied in the Netherlands before earning a law degree from the University of Virginia Law School. He worked at the Suffolk County, Massachusetts, district attorney's office in Boston, Massachusetts.
He seemed to have a bright political future, with a chance at becoming president, but an incident on July 18, 1969, virtually ended his ambitions.
After a party for the women who had worked on his brother Robert's presidential campaign, Kennedy drove his car off a bridge in Chappaquiddick, Massachusetts, near Nantucket Sound. Although he managed to escape, his passenger, Mary Jo Kopechne, drowned.
Kennedy did not report the incident immediately, and later pleaded guilty to leaving the scene of an accident.
Kennedy challenged incumbent President Jimmy Carter in 1980, but did poorly in the primaries and dropped out of the contest.
Edward Moore Kennedy was born in Boston on February 22, 1932.
He is the youngest of nine children of Joseph P. Kennedy, a prominent businessman and Democrat, and Rose Fitzgerald Kennedy. His father pushed his sons to excel and to reach for the presidency.
Joseph P. Kennedy held several federal government positions, including a brief stint before World War II as ambassador to Britain.
For much of his life, Kennedy has had the burden of being the only surviving son of nine children.
His oldest brother, Joe Jr., died in a plane crash during World War II when Kennedy was 12, and his two other brothers, John and Robert, were assassinated in the 1960s. A sister, Kathleen, was killed in a plane crash in 1948. Another sister, Rosemary, who was developmentally disabled, died in 2005.
His father, who suffered a stroke in 1961, died in 1969, making Ted Kennedy the patriarch of the family.
He lives in Hyannis Port, Massachusetts, with his second wife, Victoria Ann "Reggie" Kennedy, whom he married July 3, 1992. She has two children: Curran and Caroline Raclin.
He married his first wife, Joan Bennett, in 1958, and they divorced in 1982. They had three children: Edward Jr.; Patrick, now a U.S. House member; and Kara.
The most recent poignant moment in Kennedy's life may be when he helped toss the ashes of his nephew, John Jr., into the sea in 1999 after a plane crash that killed him, his wife and her sister.