By Astrid Wendlandt

PARIS, Aug 25 (Reuters) - French fashion designer Sonia Rykiel, known for her brightly coloured striped sweater dresses, has died at the age of 86, the owner of the fashion label she founded said on Thursday.

"It is a sad day but Sonia Rykiel leaves behind her an extraordinary legacy," Jean-Marc Loubier, chairman and chief executive of First Heritage Brands, the parent company of the Sonia Rykiel label, told Reuters. "She was a pioneer who helped women and society evolve."

Rykiel founded her fashion house in 1968, when France was rocked by violent student riots, with the aim of creating a counter-culture to stiff, bourgeois dress codes with inside-out stitches and extra-short skirts.

"She had invented not only a style but an attitude, a way of life and gave women freedom of movement," French President Francois Hollande's office said in a statement.

"I convey my sincere condolences to her children Nathalie and Jean-Philippe and their family and close ones who are in pain."

Born in 1930, Rykiel was one of the first designers to create tightly fitting sweater dresses that revealed women's body contours. Early adopters of her style included actresses Brigitte Bardot, Catherine Deneuve and Audrey Hepburn.

In 1995, she passed on the creative and management leadership to her daughter Nathalie, just around the time she was diagnosed with Parkinson's disease.

Rykiel wrote about her life and her illness in a book she published in 2012 in collaboration with journalist Judith Perrignon called "Don't forget that I am acting."

That year, her daughter Nathalie and her family sold control of the fashion label to First Heritage Brands, at the time called Fung Brands, an investment group backed by Hong Kong billionaires Victor and William Fung. The Asian group now also owns shoemaker Robert Clergerie and Belgian fine leather goods maker Delvaux.

The Rykiel family sold their remaining minority stake this year but Nathalie Rykiel still works as a consultant for the French fashion brand.

(Editing by Dominique Vidalon and Toby Chopra) ((astrid.wendlandt@thomsonreuters.com; 33149495440; Reuters Messaging: astrid.wendlandt.thomsonreuters@reuters.net))