The Russian cosmonaut flew in space twice as part of two historic missions.
Alexei Leonov, the first human to walk in space, died on Friday at the age of 85, Russia's Tass news agency reported.
The Russian cosmonaut made history in 1965, when he conducted the first-ever space walk while on the Voskhod-2 mission. The walk lasted 12 minutes and 9 seconds.
During the mission, his spacesuit filled with air to the point where he struggled to get back into the spacecraft.
He flew in space a second time in 1975, as part of the historic Apollo-Soyuz mission, the first US-Soviet space flight, which occurred as the two superpowers were pursuing a policy of detente during the Cold War.
Leonov trained as a military pilot before becoming a cosmonaut. He received a ‘Hero of the Soviet Union’ medal - one of the Russian state’s most prestigious awards - twice and has a small crater on the Moon named after him.
Leonov helped train other cosmonauts before retiring in 1992, a year after the Soviet Union collapsed. He devoted himself to private business and his twin passions of art and writing in later life.
Following his walk in space, he was quoted as saying: "The Earth was small, light blue, and so touchingly alone, our home that must be defended like a holy relic. The Earth was absolutely round. I believe I never knew what the word round meant until I saw Earth from space."
At the news of his death, tributes poured in from space organisations around the world, with NASA saying "his venture into the vacuum of space began the history of extravehicular activity that makes today's Space Station maintenance possible".
Though not as well known around the world as the first man in space, Yuri Gagarin, Leonov was a household name in Russia.
Tass reports he died after battling a long illness.