The German-born Austrian and American film actress died from pneumonia at her London home, said daughter Francesca Knittel-Bowyer from her second marriage, reported BBC.
She appeared in a number of German films before being signed by movie studio MGM to a three-year contract and making her Hollywood debut in 1935 with the film 'Escapade', which was a remake of one of her Austrian films.
A year later, she bagged her first Academy for her performance of the legendary theatrical impresario's wife in 'The Great Ziegfield'. Her portrayal of a Chinese peasant in 'The Good Earth' won her the second Oscar in 1937.
Rainer played actor Johann Strauss's long-suffering wife Poldi in the successful 1938 Oscar-winning MGM musical biopic 'The Great Waltz', her last big hit.
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'Dramatic School' in the same year was her last MGM film, post which she took retirement from Hollywood. The actress spent much of her post-Hollywood life living in London and made occasional appearances on film and TV.
She appeared in US small screen series 'The Loveboat' in 1984, while her last substantial film role came in 1998, opposite Michael Gambon in 'The Gambler'.
"She was bigger than life and could charm the birds out of the trees," she said. "If you saw her, you'd never forget her," Francesca said of Rainer.