Aleksei Arkhipovich Leonov (Cyrillic: Алексе́й Архи́пович Лео́нов; born May 30, 1934 in Listvyanka) is a retired cosmonaut who, on March 18, 1965 became the first person to walk in space.

Leonov was one of the 20 air force pilots selected as the first cosmonaut group in 1960. His spacewalk was originally to have taken place on the Vostok 11 mission, but this was cancelled, and the historic moment happened on the Voskhod 2 flight instead. By then, he had spent some eighteen months undergoing intense weightlessness training.

In 1968 Leonov was selected to be commander of a circumlunar Soyuz flight. However as all unmanned test flights of this mission failed, and the Apollo 8 mission already gave that point in the Space Race to the USA, the flight was cancelled.

Leonov's next trip into space was similarly significant — he commanded the Soviet side of the Apollo-Soyuz mission, Soyuz 19, the first joint mission between the Soviet and US space programmes.

From 1976 to 1982, Leonov was the commander of the cosmonaut team ("Chief Cosmonaut"), and deputy director of the Yuri Gagarin Cosmonaut Training Center, where he oversaw crew training. He also edited the cosmonaut newsletter "Neptune". He retired in 1991.

Leonov currently chairs an investment corporation in Moscow. He is an accomplished artist and his work has been widely exhibited and published.

The fictional spaceship Aleksei Leonov from Arthur C. Clarke's book 2010: Odyssey Two was named after Aleksei Leonov.