Russian writer Boris Strugatsky, famous for co-authoring Soviet-era science-fiction novels critical of the authorities with his late brother Arkady, passed away on Monday at 79, his foundation said.

Born in 1933 in Saint Petersburg, Strugatsky was educated in maths and worked in Russia's main astronomical observatory in Pulkovo before the Strugatsky brothers took to writing full-time and became quintessential science fiction figures.

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 artefacts he later sells on the market, losing his son in the final quest.

The book was censored countless times and later adapted into an acclaimed film, Stalker, by director Andrei Tarkovsky. In light of the Chernobyl nuclear catastrophe 15 years after the book was published, the words seem prophetic.

The Strugatsky writer duo broke apart with Arkady's death 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. They were characterised by strong political stances, where he frequently criticised President Vladimir Putin and called his policies a return to stagnation of the late Soviet era.

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