This is a Special Event Callsign of Gennady UX5UO to commemorate to first manned spaceflight 50 years ago.
Yuri Gagarin - Ю́рий Алексе́евич Гага́рин - made the historic flight on the 12th of April 1961 in his spacecraft Vostok. At the end of his flight of 1 hour and 48 minutes, he ejected from the craft and landed by parachutte.
Now wait for the beautiful QSL card, that can be seen on QRZ.
