Margot Kidder, the actress best known for portraying Superman's love interest Lois Lane opposite the late Christopher Reeve, has died at the age of 69.

Kidder died Sunday at her home in Livingston, Mont., the Franzen-Davis Funeral Home and Crematory confirmed.

People magazine said her cause of death is unknown.

Kidder portrayed Lois Lane, the determined and strong-willed Daily Planet reporter who falls in love with Superman, starting with 1978's Superman. She reprised the role three more times in Superman II (1980), Superman III (1983) and Superman IV: The Quest for Peace (1987).

Kidder also starred in Quackser Fortune Has A Cousin in the Bronx, The Amityville Horror, Mob Story and The White Room, among other films.

The actress suffered from mental health issues throughout her life that left her homeless in 1996.

She is survived by her daughter, Maggie McGuane.