The former first lady died today at her home in Bel-Air, California, of congestive heart failure, assistant Allison Borio told The Associated Press.
Her best-known project as first lady was the "Just Say No" campaign to help kids and teens stay off drugs.
When she swept into the White House in 1981, the former Hollywood actress partial to designer gowns and pricey china was widely dismissed as a pre-feminist throwback, concerned only with fashion, decorating and entertaining.
All along she maintained that her only mission was to back her "Ronnie" and strengthen his presidency.
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Mrs Reagan carried that charge through the rest of her days. She served as a full-time caretaker as Alzheimer's melted away her husband's memory. After his death in June 2004 she dedicated herself to tending his legacy, especially at his presidential library in California, where he had served as governor.
Her dignity and perseverance in these post-White House roles helped smooth over the public's fickle perceptions of the former first lady.
The Reagans' mutual devotion over 52 years of marriage was legendary. They were forever holding hands. She watched his political speeches with a look of such steady adoration it was dubbed "the gaze."
He called her "Mommy," and penned a lifetime of gushing love notes. She saved these letters, published them as a book, and found them a comfort when he could no longer remember her.
As the newly arrived first lady, Mrs Reagan raised more than USD 800,000 from private donors to redo the White House family quarters and to buy a USD 200,000 set of china bordered in red, her signature colour.
She was criticised for financing these pet projects with donations from millionaires who might seek influence with the government, and for accepting gifts and loans of dresses worth thousands of dollars from top designers. Her lavish lifestyle - in the midst of a recession and with her husband's administration cutting spending on the needy - inspired the mocking moniker "Queen Nancy.