"Me, I'm built for endurance, wit. Pleasures of the mind, pleasures of the body..."
- – Captain Jack
As a member of the Mars Resistance, Jack enjoyed a close friendship with Number One, the leader of the Resistance. His brother was a freighter pilot and let Jack stow aboard from time to time, using the cover of a simple merchant. Jack adored his daughter, Elysha, but kept her away from Mars.
After the end of the Second Shadow War, President Clark was still working with allies of the Shadows. The Drakh attached a keeper to Jack, an alien parasite that could not be removed and that kept his action in check. Jack could not warn anyone that he was being used to assassinate Number One. He met Stephen Franklin and Marcus Cole, two contacts from Babylon 5 sent to link up with the Resistance, and led them into the underground tunnels where the resistance was gathered. His keeper forced him to switch their real ID cards with fake ones, intending for them to be killed.
Jack attempted to warn the others of his condition, but he could not speak directly, so he tried indirect means. He nearly succeeded in shooting Number One, but Franklin and Marcus saved her and fired at Jack. Their shot struck the keeper, killing part of it and allowing Jack to regain control of himself. He grabbed a thermal grenade and fled to one of the transit tubes on the surface. Number One linked to Jack after Franklin examined the remains of the parasite and asked him to return to the base, saying she did not blame him for what he had done. However, Jack explained that the keepers grow back and he would be forced to do the creature's bidding again and possibly betray his comrades further. Before he could do just that, he detonated the grenade, killing himself and the keeper in an explosion that destroyed the entire transit shuttle.