Nancy Reagan, a former actress who fiercely advised and protected husband Ronald Reagan in his eight years in the White House, has died aged 94.

Mrs Reagan, first lady during her Republican husband’s presidency from 1981 to 1989, died on Monday morning (AEDT) at her home in Los Angeles of congestive heart failure, the Reagan Library confirmed.

She will be buried next to her husband, at the Ronald Reagan Presidential Library in Simi Valley, California, the statement said.

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“She is once again with the man she loved,” her stepson Michael Reagan wrote on Twitter.

From her famous ‘Just Say No’ campaign against drug use to a behind-the-scenes fight for gun control (unthinkable for a conservative in today’s political climate), Nancy is widely regarded as one of the most influential first ladies in history. Her husband, a hero among US conservatives, called her his “everything”.

For decades, the two were inseparable. Photo: Getty

During the Reagan presidency, she was often described by the media as “a sort of ‘associate president'” and “the second most powerful person in the White House”, according to historian Pierre-Marie Loizeau in his book Nancy Reagan: The Woman Behind the Man.

“Abigail Adams helped invent America. Dolley Madison helped protect it. Eleanor Roosevelt was FDR’s eyes and ears. Nancy Reagan is my everything,” Mr Reagan was quoted as saying by Loizeau.

An actress in her own right

She was born Anne Frances Robbins in 1921. Under the stage name Nancy Davis, she was a Hollywood actress during the 1940s and 1950s. Of her films, she later said they were “best forgotten”.

She married Reagan, then a prominent film actor, in 1952. She then served as first lady of California during his stint as state governor from 1967 to 1975, during which time she supported veterans groups and advocated for older Americans to serve as foster parents to children with special needs.

Ronald Reagan was elected to the White House in 1980 with a landslide win over incumbent Democratic President Jimmy Carter.

Her most publicised project as first lady was the “Just Say No” anti-drug campaign. After her husband developed Alzheimer’s disease, she became an advocate for discovering a cure.

Mrs Reagan was diminutive and publicly soft spoken but her strong will, high-tone tastes and clout with her husband made her a controversial figure during his presidency.

Right up until her death, Nancy was always a picture of style and sophistication. Photo: Getty

“For eight years, I was sleeping with the President, and if that doesn’t give you special access, I don’t know what does,” she famously said.

An advocate for gun control

Her most interesting, though less publicised campaign was for tighter gun control after the assassination attempt on Ronald Reagan in 1981.

In 1991, Ronald Reagan penned an op-ed in The New York Times outlining his support for The Brady Bill, which sought to enforce waiting periods, background checks and prohibitions against purchases by criminals and the mentally ill. It was named for his press secretary Jim Brady, who was severely injured in the failed assassination.

The New York Times reported that same year that Nancy’s influence was “decisive” in getting the former president to back the bill, a watered-down version of which was passed in 1993.

During his presidency, Mr Reagan also worked with the National Rifle Association (NRA) to ban fully automatic weapons through the Firearm Owners’ Protection Act — a move the NRA came to regret.

In an interview in 1985, Nancy Reagan admitted to being directly involved in the administration of the White House.

“I talk to people. They tell me things. And if something is about to become a problem, I’m not above calling a staff person and asking about it. I’m a woman who loves her husband and I make no apologies for looking out for his personal and political welfare.”

Active in politics until the end

Tiny and frail in her later years, Mrs Reagan devoted her time to caring for her ailing husband at their home in Los Angeles’ exclusive Bel Air enclave.

Nancy greets Jim Brady, who was badly wounded in the assassination attempt. Photo: Getty

She was always a stickler for protocol and detail and stoically presided over the former president’s weeklong funeral and celebration of his life in June 2004.

Mrs Reagan continued her involvement in US politics, occasionally appearing at Republican Party events.

Her death will cast a shadow over the current presidential campaign, as it is likely to remind US voters, especially Republican voters, of a time of greater civility and party unity, in contrast with the bickering, name-calling and spectacle of a nominee race dominated by Donald Trump.

President Barack Obama and wife Michelle paid tribute to Mrs Reagan in a joint statement on Monday, saying she “redefined” the role of first lady.

“Our former first lady redefined the role in her time here,” the Obamas said.

“Later, in her long goodbye with President Reagan, she became a voice on behalf of millions of families going through the depleting, aching reality of Alzheimer’s, and took on a new role, as advocate, on behalf of treatments that hold the potential and the promise to improve and save lives.”

-with AAP