The Strugatsky brothers began publishing their deeply philosophical works in the 1960s amid the country's infatuation with space travel, but their writing quickly turned away from utopian social realism, focusing on the darker sides of modernity, with a dose of satire on the Soviet system.

One of their best-known works, "Roadside Picnic", follows a protagonist who illegally ventures into the Earth's dangerous paranormal zones to look for artifacts he later sells on the market, losing his son in the final quest.

The book was censored countless times and later made into the acclaimed film "Stalker" by director Andrei Tarkovsky, and was seen as prophetic due to the Chernobyl nuclear catastrophe aftermath 15 years after its publication.

The Strugatsky writer tandem broke apart with the death of Arkady in 1991, but their works inspired generations of science fiction authors and a broad fan base that picks apart their novels for hidden philosophical meanings.

Boris Strugatsky published two novels on his own after his brother's death, which were not as widely read, and was known for his active stand on political issues, frequently criticising President Vladimir Putin and calling his policies a return to stagnation of the late Soviet era.

In 2009 he engaged in a long correspondence with jailed oil tycoon Mikhail Khodorkovsky, which was later made public, discussing the nature of authoritarianism and the future of humankind faced with global challenges like the end of oil.

Most recently he participated in political petitions demanding the release of jailed feminist punk band Pussy Riot and of protesters arrested on the eve of Putin's inauguration in May.

The writer lately had heart troubles and was in the hospital undergoing dialysis, RIA Novosti quoted a close friend who requested anonymity. The Arkady and Boris Strugatsky foundation confirmed his death on its official site.