Final answer:
John W. Young was selected to serve in the Astronaut program in 1966 as part of NASA's fifth astronaut group.
Step-by-step explanation:
The first astronaut selected to serve in the Astronaut program in 1966 was John W. Young. Young was chosen as one of the astronauts in NASA's fifth astronaut group, also known as Astronaut Group 5 or The Original 19. This group was selected in April 1966 and included notable astronauts such as Young, Charles Duke, and Harrison Schmitt. They played important roles in NASA's Apollo program, which culminated in the historic moon landing in 1969.