Margot Kidder is a person.
Margaret Ruth `` Margot '' Kidder ( born October 17 , 1948 ) is a Canadian American actress and activist . She rose to fame in 1978 for her role as Lois Lane in the Superman film series , opposite Christopher Reeve . Kidder began her career in the 1960s appearing in low-budget Canadian films and television series , before landing a lead role in Quackser Fortune Has a Cousin in the Bronx ( 1970 ) . She then appeared playing Siamese twins in Brian De Palma 's cult thriller Sisters ( 1973 ) ; in the slasher film Black Christmas ( 1974 ) ; and the drama The Great Waldo Pepper ( 1975 ) , opposite Robert Redford . After a highly publicized manic episode and nervous breakdown in 1996 , Kidder 's career began to slow .