Dark Sun: The Scorched World of Athas
Tieflings are descended from humans who bargained with dark powers for the strength to survive on Athas and destroy their enemies. Most tieflings lurk on civilization’s fringes in nomadic bands, drifting through the wastes in search of victims to rob and kill or hiring themselves out a vicious mercenaries. Small bands sometimes settle in the city-states, where they find work as enforcers, overseers, gladiators, and assassins. In cities where status is determined by personal merit, tieflings can become templars or rise to nobility.
Most tieflings believe that they carry a blood debt – the price to be paid for their ancestors’ bargain – and face an eternity of torment unless the debt is paid in their lifetime. Some assume that the debt can’t be paid and live in debauchery while they can, whereas others lead lives of virtue in hope of breaking their patron’s hold. The most dangerous tieflings are those who believe that their debt must be paid in blood, and that each soul they send into death reduces their own burden.