Valeri Vladimirovich Polyakov (27 April 1942 – 7 September 2022) was a Soviet and Russian cosmonaut. He is the record holder for the longest single stay in space, staying aboard the Mir space station for more than 14 months (437 days 18 hours) during one trip.
Polyakov was selected as a cosmonaut in Medical Group 3 on 22 March 1972. His first flight into space occurred on Soyuz TM-6 in 1988. After staying aboard the Mir space station and conducting research for 240 days, Polyakov returned to Earth aboard Soyuz TM-7. His first words upon return were "We can fly to Mars.”
Polyakov's second spaceflight, the longest human spaceflight in history, began on 8 January 1994 with the launch of the Soyuz TM-18 mission. He spent approximately 438 days aboard Mir, conducting experiments and performing scientific research. During this flight, he completed just over 7,000 orbits of the Earth. On 9 January 1995, after 366 days in space, Polyakov formally broke the spaceflight duration record previously set by Vladimir Titov and Musa Manarov six years earlier.
He returned to Earth aboard Soyuz TM-20 on 22 March 1995. Upon landing, Polyakov opted not to be carried the few feet between the Soyuz capsule and a nearby lawn chair, instead walking the short distance. In doing so, he wished to prove that humans could be physically capable of working on the surface of Mars after a long-duration transit phase.
Polyakov volunteered for his 438-day flight to learn how the human body would respond to the micro-gravity environment on long-duration missions to Mars. Upon returning from his second spaceflight, Polyakov held the record for the most total time in space. Data from Polyakov's flight has been used by researchers to determine that humans are able to maintain a healthy mental state during long-duration spaceflight just as they would on Earth.
After returning from space, Polyakov remained active in the discipline of international spaceflight, becoming a "cosmonaut-investigator" for the United States, Austria, Germany, and France during their respective space science missions to the Mir space station. He died on 7 September 2022 at the age of 80.
According to Wikipedia