Former US first lady Nancy Reagan died Sunday at 94, the Ronald Reagan Presidential Foundation and Library said.
Family spokeswoman Joanne Drake said Reagan died at her Los Angeles home due to congestive heart failure.
The foundation's website posted images of the former first lady and allowed mourners to leave condolences.
President and First Lady Barack and Michelle Obama offered condolences Sunday to the Reagan family.
"We remain grateful for Nancy Reagan's life, thankful for her guidance, and prayerful that she and her beloved husband are together again," they said in a White House statement.
Born Anne Frances Robbins in 1921, she had a successful career in Hollywood under the name Nancy Davis before marrying fellow actor Ronald Reagan in 1952. Supporting her husband's political career, she became the first lady of California in 1967 and then of the United States during his two-term presidency in 1981-89.
The couple had two children.
As first lady, she played a forceful supporting role to her husband, sometimes drawing criticism for her behind-the-scenes influence.
In one instance, she was seen whispering an answer into the president's ear as the first couple walked past reporters shouting questions.
She wrote in her memoirs about her persistent fears for her husband's safety, after he nearly died from his wounds in a 1981 assassination attempt outside a hotel in Washington.
Nancy's interest in astrology - which she allegedly tried to use to influence the presidential schedule - attracted ridicule near the end of the Reagan presidency.
"Nancy Reagan once wrote that nothing could prepare you for living in the White House. She was right, of course," the Obama's said Sunday. "But we had a head start, because we were fortunate to benefit from her proud example, and her warm and generous advice."
Ronald Reagan died in 2004 after a long bout with Alzheimer's, an event that prompted an outpouring of emotion from conservative America. His wife is to be buried next to him, after a public memorial ceremony at the presidential library.
She is often remembered for her "Just Say No" anti-drugs campaign during her White House years. Later, she was active in raising awareness about Alzheimer's.
Former president Bill Clinton and his wife, Hillary, who is the front-runner for the Democratic presidential nomination, said in a statement that they were "deeply saddened to learn of Nancy Reagan's passing."
They called her "an extraordinary woman: a gracious First Lady, proud mother, and devoted wife to President Reagan - her Ronnie. Her strength of character was legendary, particularly when tested by the attempted assassination of the president, and throughout his battle with Alzheimer's."
She leaves "a remarkable legacy of good" through her public campaigns, the Clintons said.
Donald Trump, the front-runner for the Republican Party presidential nomination, described her on Twitter as "the wife of a truly great president" and "an amazing woman. She will be missed!"