The world's first spacewalker, Russian cosmonaut Alexei Leonov, has died at the age of 85. 

NASA announced Leonov's death Friday morning as astronauts Andrew Morgan and Christina Koch emerged from the International Space Station to being a spacewalk. 

His 12-minute spacewalk on March 18, 1965, preceded the first U.S. spacewalk by Ed White by less than three months.

"A tribute to Leonov as today is a spacewalk," Mission Control in Houston reported.

NASA tweeted out a tribute clip saying that Leonov's venture into the vacuum of space began the history of extravehicular activity that makes Friday's Space Station maintenance possible. 

Leonov also was the Russian commander of the Apollo-Soyuz joint space mission in 1975, a prelude to the international cooperation seen aboard the current space station.

After the first-ever spacewalk, Leonov reflected on the historic moment. "You just can't comprehend it," he said. "Only out there can you feel the greatness - the huge size of all that surrounds us."

Russian Cosmonaut Alexei Leonov first spacewalk
Soviet cosmonaut Lt. Col. Alexei Leonov, figure at left , leaves spaceship Woskhod - 2 to become the first man to step into outer space.
ASSOCIATED PRESS

Leonov's assistant told AFP that the former cosmonaut died in Moscow after a long illness.  

The Associated Press contributed to this report. 

SOVIET COSMONAUTS
Eleven Soviet Union cosmonauts pose in Moscow during the nation's Cosmonaut Day ceremony in 1965. They are, back row, from left; Yuri Gagarin, first spaceman; Valery Bykovsky; Pavel Popovich, and Vladimir Komarov. Fron, from left, Kontantin Feoktistov; Valentina Nikolayeva; Alexei Leonov; Andrian Nikolayev; and German Titov. (AP Photo/tass)
ASSOCIATED PRESS