Actress Margot Kidder, best known for her role as Lois Lane in Superman, has died aged 69.
A funeral home in Livingston, Montana, where the actress lived, said Kidder died at her home on Sunday.
She rose to fame starring alongside Christopher Reeve in the Superman films of the 1970s and 1980s.
The Canadian-born actress acquired American citizenship in 2005, and became a political and women's rights activist alongside her acting.
The cause of her death is not yet known.
Kidder starred alongside Reeve in the 1978 film Superman and its sequels, as well as horror classics Black Christmas and The Amityville Horror.
The actress was also an outspoken critic of the Gulf War, of fracking by energy companies, and was at times a vocal supporter of Democratic party candidates.
After settling in the US state of Montana, she became a supporter of Montana Women For, a non-profit organisation which describes its goals as the "participation and empowerment of women in our democracy through education and advocacy on critical issues".
As an activist, she was arrested in 2011 while taking part in a protest at the White House against the Keystone XL pipeline, which remains controversial today.
Kidder also suffered from mental health problems, which resulted in her high-profile disappearance for several days in 1996, reports BBC.
On social media, film and superhero fans paid tribute to the actress. DC Comics, publisher of the Superman comic books, said Kidder was "the Lois Lane so many of us grew up with".
Kidder married and divorced three times. She is survived by her only child, Maggie, and two grandchildren.