"Tieflings trace their origins back to the 2nd Edition PLANESCAPE Campaign Setting. With their horns, tails, and wicked tongues, tieflings quickly became the exotic "bad boys" and "bad girls" of the Outer Planes. Sly, sexy, and a little sinister, they afforded D&D players a chance to flirt with the dark side without actually crossing the line into full-blown evil. Why play Drizzt when you could play the great-grandson of a pit fiend"
Tieflings reappeared in the 3rd Edition Monster Manual as one of the "plane-touched," inexorably bound to their do-gooder cousins, the aasimar. Forgive my bias, but I'll take horns and brimstone over sunshine and perfection any day. Sometimes it just doesn't pay to be the super good guy."