Margot Kidder, best known for playing Lois Lane opposite Christopher Reeve's Clark Kent in the popular Superman films of the 1970s and '80s, died Sunday, May 13 in Montana. She was 69. A cause of death has not been announced, but the actress is known to have suffered from bipolar disorder.

Born October 17, 1948, in Yellowknife, Canada, Kidder began her career in the late 1960s, appearing on TV shows like The Mod Squad before finding success on the big screen. The actress, who maintained a close relationship with Reeve until his death in 2004, starred in Superman, Superman II, Superman III and Superman IV, as well as the original The Amityville Horror.

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In the 2000s, following a well publicized manic episode, Kidder continued to find work on television. She appeared on a number of shows, including the popular WB series Smallville, which starred Tom Welling as a teenaged Clark Kent. Her credits also include The L Word, Brothers & Sisters, and R.L. Stine's The Haunting Hour, for which she won a Daytime Emmy for Outstanding Performer in Children's Programming.