Tieflings are the result of cults of humans that sought to bring great power into their bloodlines. Tieflings at best make most other races mistrustful and weary, and at worst make them violent and hateful. As such, most Tieflings are driven out of smaller towns, and are confined to the lowest quarters in the largest cities, often taking to crime to make a living.
Tieflings have monochromatic eyes with no pupil or sclera. Their skin can range from any "normal" colouring, and then various shades of red. They have horns that grow from their heads. Being decended form a demonif past, Tieflings have some inate magical abilities. They can see as well in dim light as a human can in bright sun, and they can perform Thaumaturgies starting at a very young age. They are also resistant to fires and heat.
Tieflings, being decended form humans are of similar heights and weights.
Tieflings age at the same rate as humans do, but can often live well into their 150th years.
Although Tieflings have no set alignment, they are often brought into evil organizations, or crime rings. They can be as evil or good as any human.
Tieflings will invariably speak Common, but due to their infernal blood they can at least understand infernal if not speak it outright.