Dianne Feinstein was the longest-serving current US Senator. Photo: AFP
By Bernd Debusmann Jr for the BBC
Dianne Feinstein, the California senator who served for more than three decades and was a trailblazer for women in US politics, has died aged 90.
Feinstein was the oldest member of the US Senate and voted as recently as Thursday.
For months the veteran Democrat had faced questions about alleged memory and cognitive issues.
In April she was admitted to hospital after a "minor fall" at her home, the latest in a series of health concerns.
In a statement, Feinstein's office said that she passed away at her home in Washington DC overnight.
"Senator Feinstein was a force of nature who made an incredible impact on our country and her home state," the statement added. "She left a legacy that was undeniable and extraordinary."
California Governor Gavin Newsom must now appoint her replacement. He had previously vowed to nominate a Black woman to serve out the remainder of her term, which ends in 2025.
Born in 1933, Feinstein grew up in San Francisco and graduated from Stanford University before being elected to the San Francisco County Board of Supervisors in 1969.
That election was the start of a long career in public service that saw her become San Francisco's first female mayor and eventually led her to become a senator in 1992.
She had previously announced plans to retire at the end of next year, but resisted growing calls for her to step down. Several prominent Democrats, including Congress members Adam Schiff and Katie Porter, have previously said they will run for her Senate seat.
In a statement after her death, US President Joe Biden said that Feinstein "made history in so many ways, and our country will benefit from her legacy for generations".
Earlier this year, she was absent from Capitol Hill for nearly three months following a case of shingles. She took on lighter duties upon her return and moved around the US Capitol using a wheelchair. She sometimes seemed confused during interviews, and in committee hearings or floor votes.
Feinstein was well known as a vocal advocate for gun control measures, and an ardent supporter of the assault weapons ban signed into law by President Bill Clinton in 1994.
In 1978, she became San Francisco's mayor after her predecessor, George Moscone, and city councilman Harvey Milk were shot dead.
As a senator, Feinstein was the first woman to chair the powerful Senate Intelligence Committee, where she led a years-long review of the CIA's controversial interrogation programme of foreign terrorists in the wake of the 9/11 attacks in 2001.
The review ultimately led to legislation barring the use of "enhanced interrogation techniques" such as waterboarding on terrorism suspects.
Feinstein was also the first woman to sit on the Senate Judiciary Committee, and first female chair of the Senate Rules Committee.
In a 2017 interview with CNN, she said that "being a woman in our society even today is difficult".
"I know it in the political arena," she said. "We went from two women senators when I ran for office in 1992 to 24 today - and I know that number will keep climbing."
On Capitol Hill, she was known as a centrist willing to work with her Republican opponents - sometimes leading to criticism from the more left-leaning members of her own party.
Tributes poured in from colleagues on both sides of the political spectrum.
In a statement, California Democrat Nancy Pelosi called Feinstein a "pioneering woman leader".
"Dianne's extraordinary career will inspire countless women and girls to pursue public service for generations to come," she said.
Speaking on the Senate floor, Republican minority leader Mitch McConnell praised "her dogged advocacy and diligent service".
In recent years, worries over her declining health and cognitive abilities led some to call for her retirement and highlighted concerns over America's aging politicians.
In one widely circulated video, people around her could be heard instructing her to "just say aye" during a committee vote.
She is survived by a daughter, Katherine, who reportedly has held power of attorney over her mother's legal affairs amid mounting family tensions. Her husband, investment banker Richard Blum, died last year.
* This story was first published by the BBC.