Margot Kidder, who rose to international notoriety after portraying Lois Lane in Superman: The Movie alongside Christopher Reeve, has passed away at age 69.
The Canadian-born actress was found dead at her home in Livingston, Montana on Sunday; her cause of death remains unknown. Funeral arrangements are pending.
Kidder's involvement in the 1978 film Superman: The Movie catapulted her into the limelight, eventually nabbing roles in The Amityville Horror (1979) and Heartaches (1981).
The actress notoriously battled with manic depression that resulted in terrible mood swings, and was effectively detained by police after having been reported missing for days back in 1996. Speaking with PEOPLE eight months after this much-publicized incident, Kidder revealed how "it’s very hard to convince a manic person that there is anything wrong with them. You have no desire to sleep. You are full of ideas."
In the wake of this personal battle, Kidder guest-starred on the hit CW series Smallville, as well as landing a role in the hit Broadway production The Vagina Monologues.
She is survived by her daughter, Maggie McGuane.
