The father of John Crichton, Jack Crichton is a bit of a legend in the IASA, and a hero to his son. John often said he could never be his father's kind of hero, but Jack taught him to be his own kind of hero.
One of the astronauts to land on the moon, Jack has been on several shuttle flights, often surviving by "guts, and the seat of the flight-pants". However, he was always running missions and errands, never getting the opportunity to test his own theories and experiments, something that John and D.K. set out to do, which makes him proud of his son.
The love of Jack for his son is strong, so strong that Jack was present at IASA mission control on John's fateful flight in the Farscape 1 module, alongside D.K. He took his son fishing many times, once even on the day that man landed on the moon, and at one point commandeered a jet so he could fly over to see John for his birthday.
When Jack was recreated by the Ancients from John's memories of Earth, he was idealised partially. Jack would do anything for his son, even risk security breaches and possible capture and torture. This was shown in his recreated form, but perhaps exaggerated. Later on, in season 3, the Ancient Jack returned to help them against Furlow and her alliance with the Scarrens, but was killed by Furlow.
But in the Scarran-induced version of Earth, his father at one point was angry with his son's failings, and with John's mother who had died numerous years ago.
It is unsure as to whether the real Jack Crichton will reappear in Farscape, since all that has occurred between have been memories or imperfect recreations. John has apparently been leaving cassettes salvaged from Farscape 1 floating in space for him to find. However, from the universe created in Farscape, there is no way of knowing if he has gotten any of them.