Margot Kidder, the actress who played Lois Lane in "Superman," died Sunday in Montana, TMZ reports.

Margot was at her home when she passed away, according to the spokesperson at Franzen-Davis Funeral Home in Livingston, MT. The cause of death is unknown.

Margot starred opposite Christopher Reeve in 1978's "Superman," and also in the 3 sequels. She continued acting right up until 2018, taking small roles in TV shows and movies -- but also had stage roles, including "The Vagina Monologues" on Broadway. She reportedly had 2 more roles yet to be released.

Margot had a very public battle with bipolar disorder for years. During her struggle she was briefly homeless in 1996. Margot became an advocate for mental health after that incident.

Margot is survived by a daughter.