Tales from Elrond
Rare in numbers and presence in civilized societies (with only Half-Orcs and Aasimar rarer), Tieflings are humans with a fiendish heritage (from either exposure to powerful fiendish magic or curses or from unholy unions between humans and devils). While many legends and religious scholars claim that Asmodeus is the progenitor of all Tieflings (and many Tieflings like to voice this lineage to the premier power of the Nine Hells to support their claims of prestige, power, etc over other races), this is not true. Surely many are indeed descended from Asmodeus, but others are descended from prominent devils (such as Dispater, Mammon, and Mephistopheles).
Because of their fiendish heritage, Tieflings face mistrust and suspicion and it is only due to their inherent charismatic nature that they have a been able to earn a basic acceptance into the greater society. Despite their fiendish heritage, Tieflings are free to choose their own path and there are good, evil and neutral aligned individuals amongst their populace.
Some Tieflings wish to create a Tiefling kingdom, much like the ancient Dragonborn kingdom of Gol’redar, to call home and be free of the prejudices they face from the other races, but some point to Gol’redar’s evevtually destruction as why that idea is folly and Tieflings should just work on acceptance within the existing society.