Margot Kidder, the actress who memorably played Lois Lane in the Christopher Reeve Superman movies, died at her home in Montana on Sunday. She was 69. TMZ reports that the actress’s cause of death has yet to be determined.

Although Kidder is most famous for playing Lois Lane, a whip-smart and dogged journalist who won’t allow Superman to outshine her, Kidder played several other notable roles over the course of her career. Prior to her true breakout role in the 1978 Superman movie, she played conjoined twins in the critically acclaimed psychological horror film Sisters and had a big part in the cult classic slasher flick Black Christmas. In 1979 she landed another major horror role, this time playing one of the leads in the original, sublimely creepy Amityville Horror.

Kidder was born in Canada on October 17, 1948 but became a naturalized US citizen in 2005. Her acting career stalled in the ‘90s after suffering a mental breakdown as a result of a manic episode. Kidder, who was bipolar, disappeared for four days after her computer crashed and she lost three years worth of drafts for an autobiography she had been working on.

Kidder was able to get medical help and recovered, going on to become an advocate for mental health. She returned to acting as well, appearing on Broadway in The Vagina Monologues in the early ‘00s, and in 2015 she won an Emmy award for Outstanding Performer in Children’s Programming for her performance in R.L. Stine’s The Haunting Hour.

Although she famously played Lois Lane in Superman and Superman II (making cameos in III and IV), that wasn’t her only role in the Superman franchise. In 2004 she appeared in several episodes of the TV show Smallville, playing Bridgette Crosby, an associate of a scientist played by her former co-star Christopher Reeve.

Photos via Warner Bros.