Sergei Krikalev is a Russian cosmonaut and engineer, known for his significant contributions to space exploration. Born on August 27, 1960, he flew on six space missions, including long-duration stays aboard the Mir space station and the International Space Station (ISS). He holds the record for the most time spent in space by a human, totaling over 803 days. Krikalev began his career as a test pilot before joining the Soviet space program in 1985. His missions have included important scientific research and the assembly of the ISS. He is celebrated for his expertise and dedication to advancing human spaceflight.