Boris Strugatsky, the Russian science-fiction writer who co-authored many Soviet-era novels including “Roadside Picnic” with his late brother Arkady, passed away on Monday, according to his foundation. He was 79.

The cause of Strugatsky’s death was not immediately made public: one friend of his told the Russian International News Agency that he had died from heart problems, while fellow Russian author Nina Katerli claimed the culprit had been blood cancer.

Strugatsky was born in 1933 in St. Petersburg, Russia, although it was known then as Leningrad. He graduated from Leningrad University in 1955, where he studied astronomy, and took a position as an astronomer at the Pulkovo Astronomical Observatory near St. Petersburg. He later worked as a computer programmer until he eventually gave up a career in science altogether to write full-time with his brother.

The Strugatsky brothers, as they were known internationally, helped to define the burgeoning Soviet science fiction genre: their novels included themes of space travel, philosophy, and the negative consequences of modernity. Their novels often satirized the Soviet system, and were consequently censored by the government.

In total, the two brothers published 27 books between 1958 and 1988, which were translated into 42 languages. Many were adapted into films, most famously “Roadside Picnic” which served as the basis for the 1979 film “Stalker” by Andrei Tarkvosky.

Their three-decade-long career together came to a sudden end in 1991, when Arkady died of liver cancer at the age of 66. Boris continued to write even after Arkady’s death, publishing two novels independently, including “Search for Designation” in 1994, and “The Powerless Ones in This World” in 2003. However, his solo novels were never as widely read.

The protagonist of “Roadside Picnic” is a character named Stalker, who guides illegal expeditions into a prohibited zone of the earth known for paranormal activity. Inside of “the Zone” his clients collect alien artifacts, which they smuggle back to sell on the black market. After the Chernobyl disaster 15 years later during which the area surrounding the nuclear reactor became a sealed zone, many Russian readers reconsidered the book as a prophetic text.

Strugatsky remained active until his death, holding seminars and even founding a science-fiction prize of his own called “The Bronze Snail.” Although Strugatsky was often vocally critical of Russian President Vladimir Putin, the Kremlin said that Putin had reached out to Strugatsky’s family and described the author as "a real intellectual authority for many generations," reported Reuters.