Short answers, pulled from the story.
James Benson Irwin was an American astronaut and aeronautical engineer who served as Lunar Module pilot for Apollo 15, which launched on the 26th of July 1971. He was the eighth person to walk on the Moon, spending 18 hours and 35 minutes on the lunar surface across three extravehicular activities.
Irwin and Commander David R. Scott discovered what became known as the Genesis Rock in the Hadley-Apennine region of the Moon. It is considered one of the most important geological finds of the entire Apollo era, made possible by the intensive geological training both astronauts received for the science-focused J-Mission.
Irwin and his crewmates carried 398 unauthorized commemorative first day covers to the Moon on Apollo 15 and sold 100 of them to a German stamp dealer to fund trust accounts for their children. NASA reprimanded the crew, and the astronauts never received any proceeds from the sales. The remaining covers were surrendered to investigators and returned in 1983.
Irwin developed bigeminy, a cardiac arrhythmia, during the final phase of Apollo 15 while working 23 consecutive hours without sleep. Flight surgeon Charles Berry noted that zero gravity and 100% oxygen actually placed Irwin in near-ideal conditions equivalent to an ICU. After returning to Earth he suffered three major heart attacks and ultimately died on the 8th of August 1991 following a bicycle ride.
Irwin retired as a colonel in 1972 and founded the High Flight Foundation, spending approximately two decades as what he called a "Goodwill Ambassador for the Prince of Peace." Beginning in 1973 he led multiple expeditions to Mount Ararat in Turkey searching for physical remains of Noah's Ark.
James Irwin died on the 8th of August 1991, twenty years and one day after his return from the Moon, following a heart attack after a bicycle ride. He is buried at Arlington National Cemetery and was the first of the twelve Apollo moonwalkers to die.