"Arne was a very open-minded person, not very orthodox, and interested in many fields," his editor Erling Kagge told AFP, confirming that Norway's foremost philosopher of the 20th century had died in his sleep late Monday.

"In addition to being an internationally respected philosopher, he had become in Norway an important public person concerning how people regarded themselves," he said.

Born in Oslo in 1912, Naess received his philosophy degree from the University of Oslo in 1933 before continuing his studies in Paris and Vienna.

Naess, who at the age of 27 became the youngest person ever to hold a professorship at the Oslo university, was deeply influenced by 17th century Dutch philosopher Benedict de Spinoza and was drawn to theories grounded in nature and ecology.

He developed the concept of "deep ecology," according to which humankind is simply considered an integral part of the global environment.

"Deep ecology is a movement where you not only do good for the planet for the sake of humans, but also for the sake of the planet itself," Naess said in an interview published on the University of Oslo's website.

Also a famous mountaineer, Naess in 1950 led the first expedition to reach the 7,708-metre (25,288-foot) peak of Tirich Mir in Pakistan.

As a pacifist and activist, Naess did not shy away from direct actions, like the time in 1970 when he joined a group of demonstrators who chained themselves in front of the Mardal waterfall on Norway's western coast, successfully blocking plans to build a dam there.

Just over a decade later he participated in a similar attempt to stop the planned damming of the Alta river in northern Norway, but the action failed.

Naess, who was the married father of two, was also the uncle of financier, mountaineer and ex-husband of singer Diana Ross, Arne Naess Jr., who died in a climbing accident in 2004.

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