Her 73-year marriage was the longest of any presidential couple
Former US first lady Barbara Bush has died aged 92, a family spokesperson has said.
Jim McGrath, spokesman for former president George HW Bush, said Mrs Bush had died on Tuesday.
Mrs Bush was the wife of the former president, who served from 1989 to 1993, and also the mother of George W Bush - who was president from 2001 to 2009.
The family's statement called her a "relentless proponent of family literacy".
She was one of four children, born Barbara Pierce in the New York suburb of Rye on June 8th 1925.
Her father was president of publishing company McCall's, but her mother died in a car accident in 1949.
She was 16 when she met George HW Bush at a school dance and the two married three years later in 1945, while he was on leave from wartime service.
She often said: "I married the first man I ever kissed", and together their 73-year marriage was the longest of any presidential couple.
Mrs Bush's plainspoken manner and lack of pretence at times made her more popular than her husband.
"What you see with me is what you get. I'm not running for president - George Bush is," she told the Republican convention in 1988.
She had six children - one of whom died of leukaemia aged three - and proved fiercely loyal to her husband.
Mr Bush, in turn, was fiercely loyal to her, describing himself as a "nervous wreck" when she had open-heart surgery in 2009.
After she regained consciousness, he battled back tears of relief, telling reporters about the "reunion of two people who love each other".
Despite being the wife of one president and mother of another, she drew the line at the prospect of a third Bush - Jeb - running for the White House in 2016, saying: "We've had enough Bushes."
In a 1990 commencement speech at Wellesley College, she alluded to a female US president.
"Who knows: somewhere out in this audience may even be someone who will one day follow in my footsteps and preside over the White House as the president's spouse - and I wish him well."
Barbara Bush, 1990 Wellesley College commencement speech:— Greg Hogben (@MyDaughtersArmy) April 18, 2018
"Somewhere out in this audience may even be someone who will one day follow in my footsteps and preside over the White House as the president's spouse - and I wish him well."#BarbaraBush pic.twitter.com/PWSynKVSNL
She also criticised current US President Donald Trump in a 2016 CNN interview:
In a tribute to his mother, Jeb Bush said: "I'm exceptionally privileged to be the son of George Bush and the exceptionally gracious, gregarious, fun, funny, loving, tough, smart, graceful woman who was the force of nature known as Barbara Bush."
Former president George W Bush said after his mother's death that the family's "souls are settled because we know hers was".
He described Mrs Bush as a "fabulous lady and a woman unlike any other who brought levity, love and literacy to millions".
She had "kept us on our toes and kept us laughing until the end", he said.
Barack Obama, who succeeded George W Bush as president, described Mrs Bush as "the rock of a family dedicated to public service".
He added: "We'll always be grateful to Mrs Bush for the generosity she showed to us throughout our time in the White House, but we're even more grateful for the way she lived her life - as a testament to the fact that public service is an important and noble calling; as an example of the humility and decency that reflects the very best of the American spirit."
Our statement on the passing of Former First Lady Barbara Bush: pic.twitter.com/MhTVYCL9Nj— Barack Obama (@BarackObama) April 18, 2018
Bill Clinton, who took on the role of president after George HW Bush, called Mrs Bush a "remarkable woman" who "had grit & grace, brains & beauty".
Barbara Bush was a remarkable woman. She had grit & grace, brains & beauty. She was fierce & feisty in support of her family & friends, her country & her causes. She showed us what an honest, vibrant, full life looks like. Hillary and I mourn her passing and bless her memory.— Bill Clinton (@BillClinton) April 17, 2018
In a statement posted on current president Donald Trump's Twitter page, the White House said: "As a wife, mother grandmother, military spouse and former first lady, Mrs Bush was an advocate of the American family.
"Amongst her greatest achievements was recognising the importance of literacy as a fundamental family value that requires nurturing and protection.
"She will be long remembered for her strong devotion to country and family, both of which she served unfailingly well."