The world is mourning the iconic Margot Kidder on Monday.
Kidder died on Sunday at her home in Livingston, Montana, PEOPLE has confirmed. She was 69. Her cause of death is unknown.
Kidder began acting in the late 1960s, but rose to fame in 1978 for her role as Lois Lane in Superman: The Movie opposite Christopher Reeve. She went on to reprise the part in the movie’s three sequels.
She also starred in several other films after the successful franchise. Her 1979 costar James Brolin remembered her after her passing.
“We had a beautiful time filming The Amityville Horror and we shared a lot of laughs. She will be missed,” Brolin said in a statement to PEOPLE.
Star Wars star Mark Hamill tweeted about Kidder: “Off-screen she was one of the kindest, most caring woman I’ve ever known.”
Kidder was one of many actresses to take on the role of Lois Lane. Smallville‘s Erica Durance, who played the part in the hit CW show about the early days of Superman, told PEOPLE meeting her was a highlight.
“I am shocked and extremely saddened to hear of Margot’s passing today,” she told PEOPLE. “For the moment my world is at a standstill as I contemplate her significance and contributions as an actress and a person. The first thing Margot ever said to me was, ‘You really hit it out of the park kid,’ referring to my performance as Lois Lane on Smallville, a compliment I cherish to this day. My heart goes out to Margot’s family, friends and fans. We have lost a true pioneer and giant of the Superman family.”
Teri Hatcher, another actress who played Lois Lane, tweeted that Kidder “led the way brilliantly.”
Other celebrities, including Joss Whedon and The Big Sick Oscar nominee Kumail Nanjiani tweeted about her death.
Danny Aiello, who starred alongside Kidder in her final movie The Neighborhood, said in a statement, “Sadly I never met her but I sat with the producer of the film watching a scene she was in. He [Frankie DeAngelo] mentioned what a sweetheart she was to work with and how professional she was. I think she was an outstanding actress and my heart goes out to her friends and family during this difficult time.”
Despite her success, Kidder battled mental health issues that left her homeless.
After being reported missing for days in 1996, police took her away in handcuffs to Olive View-UCLA Medical Center.
Kidder told PEOPLE five months later that the root of most of her problems — which include “mood swings that could knock over a building” — was manic depression. She was first diagnosed with the condition by an L.A. psychiatrist eight years prior, but she refused to take the recommended prescription of lithium, the recommended treatment.
“It’s very hard to convince a manic person that there is anything wrong with them,” said Kidder, who was working on a memoir at the time. “You have no desire to sleep. You are full of ideas.”
She is survived by her daughter, Maggie McGuane.