Cássia Rejane Eller was a Brazilian musician. She was born in Rio de Janeiro in 1962, but spent most of her adolescence in Brasília. In 1990 she returned to Rio and her recording career took off. Her most popular album is the live recording Acústico that she did for MTV Brasil (essentially the Brazilian version of an MTV Unplugged album), and her best-known hit songs are her cover of Malandragem, originally written by Cazuza and "Segundo Sol". Eller is known for her fusion of rock and MPB, and for her extremely deep and husky singing voice. She is also notable as one of Brazil's most prominent lesbian artists. Her sexuality, along with her musical style, has caused some to draw comparisons with Ani DiFranco and the Indigo Girls as well as Melissa Etheridge.

Eller died in December 29, 2001 after being rushed to hospital in Rio de Janeiro by her partner. She was admitted in a delirious and incoherent state during which she suffered a series of heart attacks; a police investigation concluded that these were due to a heart condition rather than to drug use. She was 39 years old, and at the time of her death, left a young son behind whose custody was assumed by her partner after her death.

Eller still has a devoted following in Brazil, and her popularity after her unfortunate death has continued to grow. Her music continues to be played daily on various Brazilian radio stations and her CDs are still prominently for sale in stores.

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Cássia Rejane Eller (Rio de Janeiro, 10 de dezembro de 1962 — Rio de Janeiro, 29 de dezembro de 2001) foi uma cantora e violonista do rock brasileiro dos anos noventa.

Caracterizada pela voz grave e o ecletismo musical, interpretou canções de grandes compositores do rock brasileiro, como Cazuza e Renato Russo, além de artistas da MPB como Caetano Veloso e Chico Buarque, passando pelo pop de Nando Reis e o incomum de Arrigo Barnabé e Wally Salomão, até sambas de Riachão e rocks clássicos de Jimi Hendrix, Mutantes, Beatles e Nirvana.

Teve uma trajetória musical bastante variada, porém curta, com algo em torno de dez álbuns próprios no decorrer de doze anos de carreira. Iniciou a carreira em Brasília e com uma presença de palco bastante intensa, Cássia Eller assumia a preferência por álbuns gravados ao vivo e era constantemente convidada para participações especiais e interpretações encomendadas.