Bette Davis, The Little Foxes (1941) -- William Wyler
Davis is Regina Giddens, a loveless shrew obsessed with money. She ruthlessly outwits her two scheming brothers and loathes her husband (Herbert Marshall) for refusing to share her lust for wealth. Lesson learned: don't expect her to retrieve your heart medicine. Nominated for Best Actress.
Louise Fletcher, One Flew Over the Cuckoo's Nest (1975) -- Milos Forman
Don't let the starched white outfit fool you. Authoritarian Nurse Ratched rules the nut ward with an iron fist and is more than a match for rebellious R. P. McMurphey (Jack Nicholson). Noncompliance is unacceptable. If drugs don't bring her patients into submission, there's always electro-shock therapy and lobotomies. Fletcher did Davis one better and won Best Actress.
Bette Davis, What Ever Happened to Baby Jane? (1962) -- Robert Aldridge