Margot Kidder, the Canadian-born actress who played Lois Lane in “Superman,” has died. She was 69.

The actress passed away in her Montana home. There are no details yet on the cause of her death. Kidder’s family confirmed the news with CTV News.

Kidder was born in Yellowknife in 1948. Even from a young age, she had ambitions of stardom.

“From when she was very young she was determined she was going to be famous,” Kidder’s sister, Annie Kidder, told CTV News Channel from Toronto. “She was going to be an actress, and she wanted to be a star.”

While most will remember Margot Kidder for her most iconic role, Lois Lane, from 1978’s Superman, her acting career began in the late 1960s.

After appearing in a number of television series, her run as a leading woman began after a move to Los Angeles in the 1970s, starring in cult classics like “Sisters” and “Black Christmas.”

But it was the role of Lois Lane that launched her into mainstream success. Kidder’s on-screen romance with Christopher Reeve lasted four movies, and made her a household name.

“To this day, it’s hard for me to look at anyone else as Superman and Lois Lane,” Chris Bumbray, a film critic with joblo.com, told CTV News Channel.

Bumbray believes the early Superman films paved the way for the popularity of the superhero movie genre today.

“Comic book films weren’t treated seriously back then, they were considered throw-offs,” he said. “In a way, I think the movies we have now wouldn’t exist if it wasn’t for ‘Superman: The Movie’ and Margot Kidder, for me, is a big part of why that was so successful.”

For Bumbray, one of Kidder’s other important roles came as Kathy Lutz in 1979’s “The Amityville Horror,” a franchise that is still producing films.

While Kidder continued to act until the end of her life, her life took a turn after a widely publicized 1996 nervous breakdown, when she was placed in psychiatric care before being diagnosed with bipolar disorder.

Following the breakdown, she became a fierce advocate for mental health, as well as a political activist.

“We got brought up feeling that we that we had a responsibility to have a voice – a loud voice – for justice, for fairness,” said Annie Kidder.

Bumbray said Margot Kidder’s role as an activist helped break down some barriers when it comes to how employees with mental health issues are treated.

“There really was a stigma back then,” he said. “People wouldn’t talk about it because it was dangerous for somebody’s career because they’d be seen as being unreliable. I think that we’re better off for having people…that were brave enough to admit that they were having problems.”

Kidder became an American citizen in 2005, and remained active in political protests as recently as last year, protesting the North Dakota pipeline.

“I hope she’s remembered as an advocate,” her sister said. “She was passionate for a just society, and part of that just society was recognizing how hard the struggles can be with mental illness and that we can do something about it.”

Annie Kidder says that while her sister's health hadn't been fantastic, there was no particular issues that she was aware of.