Valeri Polyakov holds the record for the longest single spaceflight, spending 437 days aboard the Mir space station.
Polyakov launched aboard Soyuz TM-18 on 8 January 1994 and returned aboard Soyuz TM-20 on 22 March 1995. His mission lasted about 14 months, allowing researchers to study the effects of very long-duration spaceflight.
The record concerns one continuous mission, not an astronaut’s total time in space. Polyakov had also completed an earlier Mir mission, so his cumulative spaceflight time was longer than 437 days. Russian cosmonaut Gennady Padalka holds the record for the greatest total time in space across multiple missions, while Polyakov remains famous for the longest uninterrupted stay.
The mission helped inform planning for future expeditions to Mars, where crews would face long periods away from Earth and limited opportunities for emergency return.