Chalduk himself is shrouded in mystery. He was a sorcerer of great power, and may have been a Necromanic Lich. He may have been of Aramayan descent. Details of his life are largely left to supposition, but he is considered to have been at least of mortal birth.
Supposedly, the bag was created when Chalduk "poured all of his darkness and hate into a single vessel". The actual nature of the vessel has been hotly debated (some historians claim that Chalduk himself is the bag, and created by a mortal sorcerer of the same name).
Contemporary accounts would seem to indicate that the bag was indeed a bag. Chalduk carried it on his belt, and would reach into it, scooping out handfuls of some dark power to use as a weapon. According to legend, any mortal who takes up the bag will become so powerful that "no weapon forged by the hand of man can bring harm upon them".