Claudia Alta Taylor Johnson, the widow of former US President Lyndon B Johnson, has died at the age of 94.
Mrs Johnson was a tireless environmental campaigner
Mrs Johnson - who was widely known as Lady Bird Johnson - died at her home in Austin, Texas, of natural causes, a spokeswoman said.
In 2002, Lady Bird had a stroke that affected her speech. Last month, she was briefly admitted to a hospital with a low-grade fever.
Her husband - who was the US president in 1963-1969 - died in 1973.
'Lady Bird bill'
She became First Lady on one of the most tragic days in American history - when President John F Kennedy was assassinated.
Lady Bird was a staunch supporter of her husband's ambitious policies of civil rights and on tackling poverty.
A popular First Lady, she was also one of the most influential, quietly advising her husband as he came under fire for escalating the Vietnam war, the BBC's James Westhead in Washington says.
But she was perhaps best-known as a tireless environmental campaigner, correspondents say.
She raised hundreds of thousands of dollars to beautify Washington, and the 1965 Highway Beautification Bill was known as the "Lady Bird bill".
On her years in the White House, she once recalled: "A lot of it was desperately painful, but on balance I loved it."
Lady Bird was born in Karnack, Texas, which was the plantation home of her parents.
She studied journalism and art and graduated from the University of Texas in 1934. She married Mr Johnson later that year.
After leaving the White House, the couple returned to live in Austin.