Short answers, pulled from the story.
Mattingly was removed from the Apollo 13 crew three days before launch because he had been exposed to German measles. He was replaced by backup Command Module Pilot Jack Swigert. Mattingly never actually contracted the disease.
Mattingly worked on the ground during the Apollo 13 emergency, playing a large role in helping the crew solve the problem of power conservation during re-entry. His technical contributions were central to bringing the crippled spacecraft and its crew home safely.
Mattingly flew as Command Module Pilot on Apollo 16, which launched on the 16th of April, 1972. While Commander John Young and Lunar Module Pilot Charlie Duke landed on the surface near the crater Descartes, Mattingly remained in the Command and Service Module named Casper, completing 64 lunar orbits and conducting 26 scientific experiments.
During Apollo 16's return to Earth, Mattingly conducted an extravehicular activity to retrieve film and data packages from the science bay on the exterior of the service module. It was the second deep-space EVA in history, performed at great distance from any planetary body.
Mattingly commanded two Space Shuttle missions. He commanded STS-4, the fourth and final orbital test flight of the shuttle, which launched on the 27th of June, 1982, and landed at Edwards Air Force Base on the 4th of July, 1982. He also commanded STS-51-C, the first Space Shuttle Department of Defense mission, which flew in January 1985.
Ken Mattingly died on the 31st of October, 2023, in Arlington, Virginia, at age 87. NASA announced his death two days later, on the 2nd of November. He had retired from the Navy with the two-star rank of Rear Admiral.