AceShowbiz - Margot Kidder, the actress who played Lois Lane opposite Christopher Reeve's "Superman", has died. The Canadian actress and activist, 69, passed away at her home in Montana on Sunday, May 13, according to TMZ.

Kidder started acting in the early 1960s and appeared in 1970 movie "Quackser Fortune Has a Cousin in the Bronx", Brian DePalma's "Sisters", "The Great Waldo Pepper" in 1975, and classic film "The Amityville Horror", but she shot to fame after starring in 1978's "Superman". She went on to appear in the film's three sequels.

She hit headlines for all the wrong reasons in the mid-1990s when her battle with bipolar disorder went public and she was discovered living homeless.

Margot got to grips with her condition and returned to acting, landing roles in TV shows like "Smallville", "Brothers & Sisters", and "The L Word". She went on to pick up an Emmy Award for her performance on the children's television series R.L. Stine's "The Haunting Hour" in 2015.

She also found success on Broadway in a 2002 production of "The Vagina Monologues".

Kidder was acting up until her death and reportedly has two projects yet to be released.

As an activist, she became an advocate for mental health sufferers and was arrested in Washington, D.C. in August, 2011 for protesting against an oil project.

Kidder was part of a group staging a rally about TransCanada Corp.'s Keystone XL pipeline plans. The campaigners were hoping to convince then-U.S. President Barack Obama to quash the $7 billion project to move oil from Alberta to America's Gulf Coast.

The protest outside the White House was broken up by police, who arrested several activists, including Kidder and her friend and fellow actress Tantoo Cardinal. The stars were charged with failing to obey an order governing protests on the sidewalk.

Margot was married three times, but sources claim she had been single since the late 1980s.

She is survived by a daughter.

Her cause of death is unknown but is currently under police investigation.