NASA astronaut Frank Borman, one of the agency’s best-known veteran astronauts, died Tuesday in Billings, Montana, the space agency said. He was 95.

NASA Administrator Bill Nelson called Borman “a true American hero.” Nelson cited among his other accomplishments, Borman was commander of the 1968 Apollo 8 mission, the first time humans flew around the moon.

Borman began his career as an Air Force officer. He was a fighter pilot, test pilot and assistant professor. Nelson said his “exceptional experience and expertise led him to be chosen by NASA to join the second group of astronauts.”

Before the Apollo mission, Borman flew aboard Gemini 7, the program that came before Apollo, and spent 14 days in Earth orbit. In that mission, Borman conducted “the first rendezvous in space, coming within a few feet of the Gemini 6 spacecraft,” Nelson said.

In 1967 before he flew to the moon, Borman served on the Apollo 1 fire investigation board investigating the fire that killed three astronauts aboard an Apollo spacecraft on the launch pad.

Borman became a special advisor to Eastern Airlines in 1969 after leaving NASA. He was later named senior vice-president of the airline’s operations group and executive vice president and general manager of the airline. In 1975, he was elected president and chief operating officer by the airline’s board of directors. He retired in 1986.

Borman visited the Marshall Space Flight Center in Huntsville in 1969 where he spoke to the workforce and met with then-Marshall Director Dr. Wernher von Braun.

Later, Borman was a special presidential advisor who traveled the world seeking support for American prisoners of war held by North Vietnam. He was awarded multiple medals during his career including the Congressional Space Medal of Honor. Borman was inducted in 1993 to the U.S. Astronaut Hall of Frame.

“His lifelong love for aviation and exploration was only surpassed by his love for his wife Susan,” Nelson said.