The native of Germany studied Aeronautics in Berlin and served as Luftwaffe on-board mechanic during the war. Like his father, he immigrated to the U.S. in 1949 and became a U.S. citizen in 1955. As an engineer, he worked for McDonnell Aircraft during the Mercury and Gemini manned space programs supervising spacecraft launch preparations at Cape Canaveral. He was the last person seen by the astronauts before liftoff. NASA astronaut Donn Eisele's popular pun "Ah, I vonder vhere Guenter Vendt" was used authentically in the movie, Apollo 13, spoken by actor Tom Hanks playing the role of Apollo 13 mission commander Jim Lovell.
After the Apollo 1 accident on the pad, Guenter Wendt was hired by the Apollo Manned Spacecraft Center contractor North American Rockwell. He had stopped "turning the lug wrench" to secure the hatches for astronaut crews with the end of the Gemini Program. However, NASA veteran astronaut Wally Schirra requested reassignment of the ever-competent and safety-obsessive Wendt specifically as the in-charge Pad Leader for Schirra's crew's Apollo 7 spaceflight. Crewmembers of the other Apollo missions shared an equal high regard for Wendt, so Wendt stayed on in the Pad Leader role through the end of the Apollo missions.
In NASA documentary films, Wendt appears as the smiling, bespeckled, thin technician in the white cap and overalls, usually standing to the right at the hatch door, clipboard in hand, or bending over seated crewmembers pulling their safety belts snug for launch.
Wendt was regarded as somewhat of a welcomed good luck figure to mission crews; as above, always the last reassuring earth-bound human face they saw, kidding with the crewmembers and wishing them a 'successful trip', as he directed completion of the complex pad 'close-out' procedures just prior to spacecraft launch. Wendt, the 'final word' for the launch tower white room 'close-out' team (responsible for loading and securing the mission crews, ensuring that spacecraft instrumentation, switches and controls were correct for launch, and securing the hatch), was fondly nicknamed "Der Führer of der Launch Pad" (from his German-English accent) by the astronauts for his efficient, disciplined, yet good-humored pad crew leadership.
He worked at the cape into the early Space Shuttle flights.
Guenter F. Wendt later served as a technical consultant for several TV and movie features and wrote in his biography The Unbroken Chain about his time at NASA. He remains a personal friend of many American astronauts, and is a recipient of NASA's "Letter of Appreciation" award.