Actress Margot Kidder, famed for her role as Lois Lane in 1978’s Superman, passed away Sunday in Livingston, Montana. She was 69.

The cause of Kidder’s death, first listed on the website of Franzen-Davis Funeral Home, is unknown.

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Born in 1948 Yellowknife, Northwest Territories, Canada, Kidder began her acting career in the late 1960s, appearing in a handful of low-budget film and television productions before her first starring role, opposite Gene Wilder, in the 1970 comedy Quackser Fortune Has a Cousin in the Bronx.

That was followed by roles in Brian De Palma’s 1973 thriller Sisters, the 1947 slasher film Black Christmas and the 1974 drama The Great Waldo Pepper before Kidder soared to icon status as Lois Lane in Richard Donner’s 1978 superhero classic Superman.

Kidder’s Lois was hard-nosed, independent and witty Daily Planet reporter who possessed an undeniable onscreen chemistry with Christopher Reeve; she edged out such actresses as Anne Archer, Lesley Ann Warren and Stockard Channing for the role. Kidder returned as Lois Lane in 1980’s Superman II, 1983’s Superman III and 1987’s Superman IV: The Quest for Peace.

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Kidder also famously starred opposite James Brolin in the 1979 supernatural horror film The Amityville Horror.

Diagnosed with bipolar disorder, Kidder experienced a widely publicized manic episode in April 1996, during which she disappeared for four days in Los Angeles, only to be discovered in the backyard of a Glendale homeowner. Around that same time, her career had begun to decline, and she experienced a period of homelessness.

She lat later appeared on such television series as La Femme Nikita, Law & Order: SVU, Smallville, The L Word and Brothers & Sisters, and in films like Halloween II and The Neighborhood.

An activist long involved in progressive and environmental causes, Kidder was arrested in 2011 in Washington, D.C., while protesting the Keystone Pipeline. She became an American citizen in 2005 in Butte, Montana.

Kidder, who over the years dated the likes of Brian De Palma, Pierre Trudeau, Steven Spielberg and Richard Pryor, was married and divorced three times: to author Thomas McGuane, to actor John Heard (for just six days) and to director Philippe de Broca. She has one daughter, Maggie McGuane, and two grandchildren.

(via TMZ)