Walter Cunningham, the last surviving astronaut from the first crewed mission of NASA’s Apollo program, has died at the age of 90. 

NASA confirmed Cunningham’s death in a press release, saying that the former astronaut passed away early Tuesday morning in Houston. Cunningham’s family further reiterated his passing in a statement to The Associated Press, saying he had “died in the hospital of natural causes.”

“Walt Cunningham was a fighter pilot, physicist, and an entrepreneur – but, above all, he was an explorer,” NASA Administrator Bill Nelson said. “NASA will always remember his contributions to our nation’s space program and sends our condolences to the Cunningham family.”

Cunningham’s first — and only — journey into space came when he piloted Apollo 7 in 1968, which became the first manned spaceflight of the Apollo program.

While Apollo 7 remains one of the lesser-known missions of the era, the mission was instrumental in laying the groundwork for the first moon landing during Apollo 11, which would occur less than a year later. Cunningham’s mission was also the resumption of NASA’s human spaceflight efforts following the deaths of three astronauts during a launch test of Apollo 1 less than two years prior.

Born in Creston, Iowa in 1932, Cunningham would fly over 50 missions as a fighter pilot during the Korean War before NASA selected him as an astronaut in 1963. He was on the prime crew for the cancelled Apollo 2 and the backup crew for the ill-fated Apollo 1 before eventually being assigned to Apollo 7.