He was recently "kind" enough to loan some money to Vano, providing him with the funds to buy a new protective suit. Jack is the leader of a group of bandits hanging out at the Checkpoint in Jupiter.
Bandits usually stay clear of the many factions as their numbers and often superior equipment are an uneven match. They often prey on stalkers who are also their primary concern as their solidarity tends to be quite strong due to the nature of bandits and their lack of respect for human life and values, there is often tension between these groups and intense fighting is very common between the two.
The unfriendly environment of the Zone also means that many bandits find peace here to conduct their illegal activities away from the watchful eye of the law. The abundance of precious artifacts has meant that a criminal element has become an ubiquitous addition to the Zone. If I have missed something or someone important, please do not hesitate to contact me. Alot of "anonymous" stalkers have been left out because they don't provide missions nor crucial information. This section contains descriptions of all the different factions that can be found in S.T.A.L.K.E.R.: Call of Pripyat, as well as information regarding key persons and contacts - these may be giving out missions, trade weapons, armor and equipment, perform modifications or repairs, or just play a more active part in the game. The Zone Survival Guide - Call of Pripyat - Persons, Contacts & Factions