Aasimar were human-based planetouched, native outsiders that had in their blood some good, otherworldly characteristics. They were often, but not always, descended from celestials and other creatures of pure good alignment, but while predisposed to good alignments, aasimar were by no means always good.
Most aasimar grew up cautious around others and, like tieflings, were sometimes misunderstood, though never to the hateful extent many of the fiendish bloodlines were. Even those raised by understanding parents could not escape their strangeness, or the curiosity (or even fear) that their unique nature sometimes provoked. Many aasimar even suffered prejudice, something that deeply hurt the soul of the aasimar in question since most had an inherent bent towards empathy for others.