Although the children of the devil have been around for centuries, the first to track down their heritage and record the bloodlines was a noblewoman from medieval Milan, known only as The Lucifuge. She sought those families who, every seventh generation, produced a child that was touched with Lucifer's power. When one presented themselves as demon-touched, she sent her messengers to them with a choice; renounce Satan or be destroyed. Those who chose the former became the origins of the Lucifuge. So they have continued since then, eventually becoming completely made of children of hell who have chosen to follow a path of righteousness over one of evil.
The Lucifuge uses their "gifts" (or curses, depending on which one you ask) to rid the world of the creatures of darkness, which they believe to have all come from Lucifer's legions. These creatures are carefully tracked and studied before the children of the Seventh Generation reveal themselves to destroy them. They are particularly effective at tracking down demons and other demon-born, and also have a surprising amount of information on angels, including such unusual phenomenon as the qashmallim.
Members can be born into the Lucifuge as children of demon-blood. If their blood is known, but their families do not follow the ways of the Lucifuge, potentials will be approached by members when their powers manifest. At any point, the Lucifuge has exactly 666 members; if one dies, another always seems ready to step up and take their place.
The lady of Milan who now calls herself the Lucifuge remains in charge of the group, still in Milan and still as beautiful as the day she started the conspiracy. She both issues commands to her agents of good and will personally talk with each and every new member to help them see their destiny, good or bad.
Most agents will have one of three philosophies towards their work. The Denial ones are the most common and the simplest in beliefs: the devil is evil, and they must do away with that evil to redeem themselves. Reconciliation members are a bit more complex; they believe they are not redeeming themselves, but rather their ancestor Lucifer so that he can rejoin God and put an end to the existence of hell. Finally, the Truth types are the rarest; they are the skeptics, curious as to the motives of the Lucifuge (both the person and the organization) and their role in the whole affair.