John Young, an astronaut who flew the first Space Shuttle mission, has died at the age of 87.

NASA announced Saturday that Young passed away the previous night following complications from pneumonia.

Young, who walked on the Moon and was the first astronaut to go to space six times, participated in the Gemini and Apollo missions.

“Today, NASA and the world have lost a pioneer. Astronaut John Young's storied career spanned three generations of spaceflight; we will stand on his shoulders as we look toward the next human frontier," acting NASA Administrator Robert Lightfoot said in a statement.

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“John was one of that group of early space pioneers whose bravery and commitment sparked our nation's first great achievements in space. But, not content with that, his hands-on contributions continued long after the last of his six spaceflights -- a world record at the time of his retirement from the cockpit."

We're saddened by the loss of astronaut John Young, who was 87. Young flew twice to the Moon, walked on its surface & flew the first Space Shuttle mission. He went to space six times in the Gemini, Apollo & Space Shuttle programs. pic.twitter.com/l4nSwUCMIq — NASA (@NASA) January 6, 2018

Young's death was marked by a statement from NASA Johnson Space Center Director Ellen Ochoa, who called Young's work "groundbreaking."

"It would be hard to overstate the impact that John Young had on human space flight. Beyond his well-known and groundbreaking missions through three programs, he worked tirelessly for decades to understand and mitigate the risks that NASA astronauts face. He had our backs," Ochoa told ABC News.

Young retired to Houston after leaving NASA. Former President and Texas native George H.W. Bush, who was friends with the retired astronaut, offered his condolences on Saturday.

"John was more than a good friend," Bush said in a statement. "He was a fearless patriot whose courage and commitment to duty helped our Nation push back the horizon of discovery at a critical time."