U.S. Senator Edward Kennedy, the youngest brother of the late U.S. President John F. Kennedy and one of the most most influential lawmakers in U.S. history, has died at the age of 77.  

Kennedy's family says he died late Tuesday at his home in the small Massachusetts town of Hyannis Port.  The Democratic senator had been suffering from an incurable form of brain cancer for just over a year.

A statement issued by the family described him as "the irreplaceable center of our family and joyous light in our eyes."

He had been missing in the U.S. Senate for much of this year due to his illness, forcing him to work on his lifelong signature issue, a national health care system, from his Hyannis Port home.

Kennedy had represented Massachusetts in the U.S. Senate since 1962, when he was elected to the seat previously held by President Kennedy.  During his Senate career, he was a strong champion of liberal causes, including civil rights, education and immigration, in addition to health care.  

President Barack Obama, who Kennedy endorsed during the 2008 presidential campaign, recently awarded the ailing senator the Presidential Medal of Freedom.

In January, the senator collapsed at a luncheon in the U.S. Capitol rotunda following the inauguration of President Obama.  

Kennedy was a strong, vocal critic of both the Vietnam War and the U.S.-led invasion in Iraq in 2003.  His passionate, unwavering commitment his views, along with his towering presence in the Senate chamber and his ability to work across the political divide, earned him the nickname "Lion of the Senate."

His personal life was marred by tragedy and scandal.  Kennedy's two older brothers, President John F. Kennedy and Senator Robert Kennedy were both assassinated.  In 1969, he was in a car accident on Chappaquiddick Island in Massachusetts that claimed the life of a female passenger.  He later pleaded guilty to a charge of leaving the scene of an accident.

His first marriage, to Joan Bennett Kennedy, ended in divorce in 1982 after 24 years of marriage.  He married his second wife, Victoria Reggie, who survives him, along with his three children from his first marriage and several nieces and nephews.

His autobiography, "True Compass," is scheduled to be published sometime next month.  Much of the source material for the project will come from an oral history project he has been participating in with the University of Virginia since 2004.