Send this page to someone via email

Margot Kidder, the actor best known for playing Lois Lane in the ’70s and ’80s Superman movies alongside Christopher Reeve, died on Sunday. She was 69 years old.

The cause of her death is unknown, though her representative confirmed she passed away “peacefully” in her sleep. A spokesperson at Franzen-Davis Funeral Home in Livingston, Mont. also confirmed Kidder’s death.

“We’re sad,” said a clearly devastated Annie Kidder to Global News. “We and her family are all shocked, we just found out. It happened yesterday afternoon. We’re sad and surprised.”

READ MORE: Pauley Perrette hints at physical abuse, bullying on set of ‘NCIS’

She’d been living in Montana for at least 25 years, along with her daughter Maggie and her grandchildren. She became a U.S. citizen in 2005.

Story continues below advertisement

Kidder was born in Yellowknife, N.W.T. on Oct. 17, 1948, one of five children. (Her sister, Annie Kidder, resides in Toronto and works for Canadian registered charity People for Education. A brother, Michael Kidder, lives in Vancouver.) She travelled a lot as a child because of her father’s job, and spent a few years as a child in Labrador City, Newfoundland and Labrador. She went to multiple schools and eventually graduated from Toronto’s Havergal College in 1966.

WATCH: Margot Kidder, known as Lois Lane in ‘Superman,’ died at 69

0:31 Margot Kidder, known as Lois Lane in ‘Superman,’ dies at 69 Margot Kidder, known as Lois Lane in ‘Superman,’ dies at 69

She got a taste of showbiz when her mother took her to New York when she was 12. It was a sign for the impressionable Kidder.

“We didn’t have movies in this little mining town. When I was 12 my mom took me to New York and I saw Bye Bye Birdie, with people singing and dancing, and that was it,” she said to The Guardian in 2005. I knew I had to go far away. I was clueless, but I [have done] OK.”

Story continues below advertisement

She catapulted to fame for her performance as a journalist and Superman’s love interest, Lois Lane, in 1978’s Superman. She went on to star in Superman II, III and IV.

WATCH: Hollywood reacts to the death of Margot Kidder

1:07 Hollywood reacts to the death of Margot Kidder Hollywood reacts to the death of Margot Kidder

READ MORE: Drake announces 41-date tour with Migos

Kidder became an advocate for mental health issues after speaking out about living with bipolar disorder. She had an infamous breakdown on the streets of Los Angeles in 1996.

She credited a homeless man with showing compassion for her and saving her life during her “big, public flipout.”

“We are all … a breath away from mental illness, homelessness, all of these things we tend to so look down on,” Kidder said in 2006. “We are all one human family and we really have to take care of each other.”

Story continues below advertisement

She also became a political activist in recent years and was among a group of environmentalists to be arrested outside the White House in 2011 during a protest against TransCanada’s Keystone XL pipeline.

Kidder had settled in Montana to live in a “culture-free zone” away from the spotlight.

Hollywood personalities took to Twitter to share their condolences at her passing.

The Reeve Family and Foundation are deeply saddened by the loss of Margot Kidder. Fly high, our friend, shine bright. #Superman pic.twitter.com/EYWWevThQN — Christopher & Dana Reeve Foundation (@ReeveFoundation) May 14, 2018

On-screen she was magic.

Off-screen she was one of the kindest, sweetest, most caring woman I've ever known.

I'll miss you #MargoKidder.

Your legacy will live on forever. pic.twitter.com/UBlbszEIhb — Mark Hamill (@HamillHimself) May 14, 2018

oh no, Margot Kidder. — Elijah Wood (@elijahwood) May 14, 2018

RIP Margot Kidder. One of my favorite movies of hers is the original Black Christmas. It introduced some elements that are now genre tropes and she’s fantastic in it. — Kumail Nanjiani (@kumailn) May 14, 2018

My Lois Lane has passed away. RIP Margot Kidder. Thank you for my favourite movie ever. pic.twitter.com/dUmxwOUjyi — Mark Millar (@mrmarkmillar) May 14, 2018

The only Lois Lane I acknowledge #RIPMargotKidder pic.twitter.com/lrglXJr8co — Eric Haywood (@EricHaywood) May 14, 2018

Superman was a superhero blockbuster two decades before comic book movies became the norm at the top of the box office.

Both Kidder and co-star Reeve, who played Superman, were relative unknowns when they got their leading parts, and neither saw many major roles afterward. Reeve died in 2004 after becoming paralyzed in a horse-riding accident.

Kidder also appeared in 1975’s The Great Waldo Pepper with Robert Redford and 1978’s The Amityville Horror.

She continued to work in TV and film despite her struggles, and won a daytime Emmy in 2015 for outstanding performance in a children’s or preschool series for R.L. Stine’s The Haunting Hour.

Story continues below advertisement

READ MORE: Drake announces 41-date tour with Migos

She appeared in stage productions such as The Vagina Monologues and Love, Loss and What I Wore.

Kidder was married and divorced three times and was also famously linked to former prime minister Pierre Elliott Trudeau. Kidder was credited with influencing Trudeau’s decision to launch a global peace initiative during his final months in office, according to the 2009 biography Just Watch Me: The Life of Pierre Elliott Trudeau 1968-2000.

Annie said that Kidder’s health had not been great recently, but any problems were mostly due to aging. An autopsy is scheduled to be performed. As of this writing, there is no additional funeral information.

— With files from The Canadian Press