In the hope of locating a suitable new world for his people to call home, "Jack" created a false Earth out of John Crichton's memories. John discovered the deception, and confronted "Jack". He explained the situation, that his people were slowly dying and needed to find a new home, but that they had deemed Earth too hostile to extraterrestrials.
Unbeknownst to Crichton, "Jack" had deposited a wealth of knowledge of wormholes in his subconscious. This knowledge would later be uncovered by Scorpius, and make Crichton the most wanted man in the Milky Way.
More than two cycles later, the Ancients sensed Farscape-1 in a wormhole, being piloted by a Charrid. Believing Crichton had given away the dangerous wormhole knowledge they had imparted, "Jack" reappeared to Crichton. Together, they discovered that Furlow had reconstructed the module. They learned, however, that she had been betrayed by her prospective clients and that the Scarrans were enroute to retrieve her wormhole technology. To prevent this, "Jack" constructed a wormhole weapon -- however, Furlow betrayed them and killed "Jack" before he could use the weapon.
"Jack" the Ancient appeared in episodes of the first and third seasons of the series Farscape.