Tiefling
Tieflings are mortals touched by the dark energies of the Lower Planes. They are perhaps the best-known planetouched.
Tieflings are not to be confused with cambions, which are half-humans, half-fiends.
Development
The tiefling "gene," so to speak, can lay dormant across generations. It's possible—and, in fact, often the case—that tieflings are born to completely ordinary human families who haven't had a tiefling in the family for centuries.
The "gene" can also lay dormant until later in life: many (if not most) tieflings are born looking like ordinary humans, and only around puberty do their horns come in and skin change in color.
Social status
Tieflings are often viewed with suspicion and even open hostility. In Riyan, for instance, tieflings are second-class citizens. In Alicante, they are killed on sight.