Harper was 80 years old, and a cause of death is not yet known.
Harper played the down-on-her-luck, down-on-herself single Jewish girl who had left the Bronx for Minneapolis - "where it's cold", Rhoda later explains, "and I figured I'd keep better".
She won three Primetime Emmy Awards for Outstanding Supporting Actress in a Comedy Series and another for Lead Actress for her work on Rhoda.
Harper and Moore got together for the TV-movie Mary and Rhoda, reprising their beloved sitcom roles.
"I know a lot of you feel like you know me, that you are part of the Morgenstern family and I feel I know you too and so I owe you the truth at the same time as everybody else", Harper told "People" in 2013.
But just like Rhoda, the spunky, wise-cracking best friend of Moore's Mary Richards, Harper didn't back down from a fight. "Aunt Paula" was as wonderful to work with as she was amusing.
SAG-AFTRA president Gabrielle Carteris said in a statement, "Valerie Harper was a wonderful actor who made us laugh and cry and laugh again". The episode featuring Rhoda's wedding to Joe (David Groh) in 1977 was one of television's highest rated series earning 52 million viewers. If you've never seen her work, do yourself a favour and watch "The Mary Tyler Moore" (available on Hulu) and the spinoff "Rhoda".
Harper first achieved success as a dancer on the stage before TV beckoned, appearing in the Broadway productions of Take Me Along, Wildcat (with Lucille Ball), Subways Are for Sleeping, Something Different, and Paul Sills' Story Theatre. However, she survived for almost/over six years thanks to her medical care.
Harper was diagnosed with an incurable form of brain cancer in 2013.
Harper guest-starred on such programs as Sex and the City, Desperate Housewives, and Drop Dead Diva.
"Every five minutes, every hour, every day, every year that you waste worrying about your cancer - you have forfeited time that you could have been alive having fun", she told Closer Weekly in 2015.
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