Atop the Shoulders of Giants
The Tiefling are those people who have traces of demonic blood in their veins, usually from a grandparent or great grandparent, though sometimes from multiple, more distant, ancestors. Aside from their demonic heritage, Tiefling can be of any humanoid race (and possibly many non-humanoid races), and can freely inter-breed as if they were a member of their non-celestial race, often producing more Tiefling depending on the potency of their fiendish heritage.
Ultimately Tiefling are less of a race to themselves as they are a modified member of an existing race. It is as valid to say that someone who is of elven descent who is a Tiefling is an “Elven Tiefling” as it is to say simply that they are an “Elf” or simply that they are a "Tiefling.” Each statement is true, with varying amounts of information.
Generally speaking it is not difficult to discern that someone is a Tiefling as they tend to have strange skin and eye colors. Skin tones tend to include red, orange, yellow, or green, whereas eye include vibrant reds, blues, and purples with an incredibly high rate of heterochromia, usually occurring as one eye of a normal eye color for the race while the other is a completely unusual or unnatural color.
Tiefling tend to have extended life spans compared to other members of their race, usually living about 20% longer than the average member of their race, though there have been some who lived up to 160% of their races’ normal lifespan.
Many people tend to believe that Tieflings are cursed and that their passing and presence is an ill omen. In some places, Tieflings are also thought to be evil, perverted at a metaphysical level by their demonic heritage.
In truth no evidence exists that Tieflings tend to be evil or tend to have misfortune follow in their wake, but these perceptions do lead to a very large number of Tieflings either living alone or engaging in illicit professions – as no one wants to engage them to undertake a legitimate business.