Russian cosmonaut Valery Polyakov has died at the age of 80, officials say. The Russian space agency Roskosmos announced on Monday "with regret the death of Hero of the Soviet Union, Hero of Russia, Soviet pilot and cosmonaut and world record holder for the longest flight into space (437 days) Valery Polyakov". Polyakov was a doctor and had been part of the Soviet space program since the 1970s. As a cosmonaut, he flew twice to the Mir space station in the 1980s and 1990s.

During the Soyuz TM-18 space mission from 1994 to 1995 he was in space for a total of 437 days, 17 hours and 58 minutes. He still holds the world record for a long-term stay. In total, Polyakov spent more than 678 days in space.

However, unlike most of his colleagues, the cosmonaut never left the space station for an outdoor mission in the open cosmos. Polyakov wrote more than 50 scientific papers on space medicine. The family father leaves behind a wife and daughter as well as two grandchildren.