Short answers, pulled from the story.
Young is the only astronaut to have flown four different classes of NASA spacecraft: Gemini, the Apollo command module, the Apollo Lunar Module, and the Space Shuttle. He is also the only person to both walk on the Moon and fly on the Space Shuttle.
During the Gemini 3 flight on the 23rd of March 1965, Young smuggled a corned beef sandwich aboard. He and commander Gus Grissom shared it while testing food in orbit. The House Committee on Appropriations held a hearing on the incident, with some members arguing the two astronauts had disrupted a scheduled food experiment.
Shortly after Young and Duke undocked the lunar module, Ken Mattingly reported a problem with the thrust vector controls on the service propulsion system of the command module. This would have prevented the command module from maneuvering if the lunar module could not complete its rendezvous. Mission Control approved the landing after a delay, pushing the surface work 5 hours and 42 minutes behind schedule.
After the Challenger disaster, Young testified before the Rogers Commission and criticized NASA's safety culture. He was reassigned from Chief of the Astronaut Office in May 1987 to Special Assistant to Johnson Space Center Director Aaron Cohen for Engineering, Operations and Safety. He oversaw the redesign of the solid rocket boosters and advocated for drag parachutes, GPS navigation, and stronger thermal protection tiles.
Young retired from NASA on the 31st of December 2004, after 42 years of service. After retirement he worked as a public speaker and advocated for asteroid impact avoidance, lunar colonization, and climate engineering. In 2012, he co-authored his autobiography, Forever Young, with James R. Hansen.
Asteroid 5362 Johnyoung is a minor planet named in honor of John Young. It joins the S.S. John Young Cygnus spacecraft and the John Young Parkway in Orlando among the public tributes named after him.