Created when the Chelaxian Kingdom bargained with 10 different demon lords to gain power to overcome the invading Tudor Kingdom. This created 10 separate lineages of Tieflings.
The original Progenitors of the Tiefling race were the 14 Chelaxians in the throne room during the Bargaining, if one of the Progenitors die, then their entire line dies with them.
Progenitors are immortal, and can only be destroyed by the Dagger of Princess Jael the dagger that created them in the first place by the Sacrifice of Prince Gwen Tudor