LAST EDITED ON May-15-18 AT 04:01 AM (EDT)
While no actual cause has been give, her publicist has stated she passed in her sleep.And yes, Lois Lane is, of course, the most well known of her roles, but she did many others and also other than acting. RIP, indeed.
Edit to add a really good obit from The Guardian: https://amp.theguardian.com/film/2018/may/14/margot-kidder-death-superman-lois-lane-defied-convention
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Stoke Mandeville, Esq & The Victorian Ballsmiths
"Nobody Want Verdigris-Covered Balls!"