Tales of the Inner Sea
The details of the origin of the Tieflings is a secret closely guarded by the Empire of Tharn. It is generally accepted that they are descended from humans that were either bred with devils or perhaps fiends of some other sort, or else were in some other way infected with infernal energy, as part of a secret project by the Tharnish priesthood. The details are not even known by most Tieflings themselves. The only thing that is passed down amongst them is that the project was some sort of attempt to create the perfect soldier, and that while the result wasn’t a complete failure, the beings it produced showed generally the same range of capabilities and personality traits as other prospective recruits. Although there are some hard feelings about the experiments done on their ancestors there, most Tieflings have remained in Tharn, mostly because they’re more or less accepted there. A few families even retain their ties to the military and have a strong, respected tradition of service. They are generally unwelcome in elven and dwarven lands, and the more rustic northern kingdoms tend to be very superstitious and are thus wary as well. Due to the existence of certain cults, Carcosa is a strong draw for those Tieflings who are, in fact, guilty of all the things they’re commonly accused of, which makes it a singularly unsavory place for the majority of Tieflings who are really just ordinary people with horns and tails. As for Etro, which is quite cosmopolitan and would ordinarily be just the place for a Tiefling family looking for a fresh start, most have avoided the place for a surprising reason. The following quote is from the closing portion of a letter addressing ongoing treaty negotiations from the Tharnish Tiefling general Baal Han to the Etric counselor, Oran:
Lasly, I hesitate to mention this as it is a personal matter and has no direct bearing on the current negotiations. Nevertheless, I wish to bring up a number of strange and deeply disturbing correspondences that Tiefling communities and families have been receiving from your imperial academy in the gnomish hills. They all express a certain excitement about meetings and vaguely defined events and offer to pay us for attending the university, so that ‘we may have the unique opportunity to learn from one another.’ While the cynical might call this too good to be true, I’m certain the more facile among us would have journeyed there already were it not for the fact that they also offered ‘handsome reimbursement to family and loved ones should our academic interaction produce unfortunate and, we assure you, utterly unforseen consequences.’ While I grant that our lack of knowledge of gnomish culture could be causing us to misinterpret such statements, Its worth pointing out that a common belief amongst our Tiefling communities that your gnomes want to use us as experimental subjects is not conductive to long term peace, particularly considering our origins and certain existing sensitivities.